KSH(1) General Commands Manual KSH(1)
NAME
ksh, rksh - KornShell, a standard/restricted command and programming
language
SYNOPSIS
ksh [ ±abcefhiklmnprstuvxBCDEGH ] [ ±o option ] ... [ - ] [ arg ... ]
rksh [ ±abcefhiklmnpstuvxBCDEGH ] [ ±o option ] ... [ - ] [ arg ... ]
DESCRIPTION
Ksh is a command and programming language that executes commands read
from a terminal or a file. Rksh is a restricted version of the command
interpreter ksh; it is used to set up login names and execution environ-
ments whose capabilities are more controlled than those of the standard
shell. See Invocation below for the meaning of arguments to the shell.
Definitions.
A metacharacter is one of the following characters:
; & ( ) | < > new-line space tab
A blank is a tab or a space. An identifier is a sequence of letters,
digits, or underscores starting with a letter or underscore. Identi-
fiers are used as components of variable names. A vname is a sequence
of one or more identifiers separated by a . and optionally preceded by a
.. Vnames are used as function and variable names. A word is a se-
quence of characters from the character set defined by the current lo-
cale, excluding non-quoted metacharacters.
A command is a sequence of characters in the syntax of the shell lan-
guage. The shell reads each command and carries out the desired action
either directly or by invoking separate utilities. A built-in command
is a command that is carried out by the shell itself without creating a
separate process. Some commands are built in purely for convenience and
are not documented here. Built-ins that cause side effects in the shell
environment and built-ins that are found before performing a path search
(see Execution below) are documented here. For historical reasons, some
of these built-ins behave differently than other built-ins and are
called special built-ins.
Commands.
A simple-command is a list of variable assignments (see Variable Assign-
ments below) or a sequence of blank separated words which may be pre-
ceded by a list of variable assignments (see Environment below). The
first word specifies the name of the command to be executed. Except as
specified below, the remaining words are passed as arguments to the in-
voked command. The command name is passed as argument 0 (see exec(2)).
The value of a simple-command is its exit status; 0-255 if it terminates
normally; 256+signum if it terminates abnormally (the name of the signal
corresponding to the exit status can be obtained via the -l option of
the kill built-in utility).
A pipeline is a sequence of one or more commands separated by |. The
standard output of each command but the last is connected by a socket-
pair(2) or (if the posix shell option is on) by a pipe(2) to the stan-
dard input of the next command. Each command except the last is run
asynchronously in a subshell (see Subshells below). If the monitor or
pipefail option is on, or the pipeline is preceded by the reserved word
time, then the shell waits for all component commands in the pipeline to
terminate; otherwise, the shell only waits for the last component com-
mand. The exit status of a pipeline is the exit status of its last com-
ponent command, unless the pipefail option is enabled. Each pipeline
can be preceded by the reserved word ! which causes the exit status of
the pipeline to become 0 if the exit status of the last command is non-
zero, and 1 if the exit status of the last command is 0.
A list is a sequence of one or more pipelines separated by ;, &, |&, &&,
or ||, and optionally terminated by ;, &, or |&. Of these five symbols,
;, &, and |& have equal precedence, which is lower than that of && and
||. The symbols && and || also have equal precedence. A semicolon (;)
causes sequential execution of the preceding pipeline; an ampersand (&)
causes asynchronous execution of the preceding pipeline (i.e., the shell
does not wait for that pipeline to finish). The symbol |& causes asyn-
chronous execution of the preceding pipeline with a two-way pipe estab-
lished to the parent shell; the standard input and output of the spawned
pipeline can be written to and read from by the parent shell by applying
the redirection operators <& and >& with arg p to commands and by using
-p option of the built-in commands read and print described later. The
symbol && (||) causes the list following it to be executed only if the
preceding pipeline returns a zero (non-zero) value. One or more new-
lines may appear in a list instead of a semicolon, to delimit a command.
The first item of the first pipeline of a list that is a simple command
not beginning with a redirection, and not occurring within a while, un-
til, or if list, can be preceded by a semicolon. This semicolon is ig-
nored unless the showme option is enabled as described with the set
built-in below.
A command is either a simple-command or a compound-command, which is one
of the following. Unless otherwise stated, the value returned by a com-
mand is that of the last simple-command executed in the command.
for vname [ in word ... ] ;do list ;done
Each time a for command is executed, vname is set to the next
word taken from the in word list. If in word ... is omitted,
then the for command executes the do list once for each posi-
tional parameter that is set starting from 1 (see Parameter Ex-
pansion below). Execution ends when there are no more words in
the list.
for (( [expr1] ; [expr2] ; [expr3] )) ;do list ;done
The arithmetic expression expr1 is evaluated first (see Arith-
metic Evaluation below). The arithmetic expression expr2 is re-
peatedly evaluated until it evaluates to zero and when non-zero,
list is executed and the arithmetic expression expr3 evaluated.
If any expression is omitted, then it behaves as if it evaluated
to 1.
select vname [ in word ... ] ;do list ;done
A select command prints on standard error (file descriptor 2) the
set of words, each preceded by a number. If in word ... is
omitted, then the positional parameters starting from 1 are used
instead (see Parameter Expansion below). The PS3 prompt is
printed and a line is read from the standard input. If this line
consists of the number of one of the listed words, then the value
of the variable vname is set to the word corresponding to this
number. If this line is empty, the selection list is printed
again. Otherwise the value of the variable vname is set to the
empty string. The contents of the line read from standard input
is saved in the variable REPLY. The list is executed for each
selection until a break or end-of-file is encountered. If the
REPLY variable is set to the empty string by the execution of
list, then the selection list is printed before displaying the
PS3 prompt for the next selection.
case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac
A case command executes the list associated with the first pat-
tern that matches word. The form of the patterns is the same as
that used for pathname expansion (see Pathname Expansion below).
The ;; operator causes execution of case to terminate. If ;& is
used in place of ;; the next subsequent list, if any, is exe-
cuted.
if list ;then list [ ;elif list ;then list ] ... [ ;else list ] ;fi
The list following if is executed and, if it returns a zero exit
status, the list following the first then is executed. Other-
wise, the list following elif is executed and, if its value is
zero, the list following the next then is executed. Failing each
successive elif list, the else list is executed. If the if list
has non-zero exit status and there is no else list, then the if
command returns a zero exit status.
while list ;do list ;done
until list ;do list ;done
A while command repeatedly executes the while list and, if the
exit status of the last command in the list is zero, executes the
do list; otherwise the loop terminates. If no commands in the do
list are executed, then the while command returns a zero exit
status; until may be used in place of while to negate the loop
termination test.
while inputredirection ;do list ;done
Filescan loop. This is defined by a lone input redirection fol-
lowing while (see Input/Output below). It is faster than using
the read built-in command in a regular while loop. The shell
reads lines from the file or stream opened by inputredirection
until the end is reached or the loop is broken. For each line
read, the command list is executed with the line's contents as-
signed to the REPLY variable and the line's fields split into the
positional parameters (see Field Splitting and Positional Parame-
ters below). Within the list, standard input is redirected to
/dev/null. If the posix compatibility shell option is on, this
loop type is disabled and inputredirection is processed like a
lone redirection in any other context.
((expression))
The expression is evaluated using the rules for arithmetic evalu-
ation described below. If the value of the arithmetic expression
is non-zero, the exit status is 0, otherwise the exit status is
1.
(list)
Execute list in a subshell (see Subshells below). Note, that if
two adjacent open parentheses are needed for nesting, a space
must be inserted to avoid evaluation as an arithmetic command as
described above.
{ list;}
list is simply executed. Note that unlike the metacharacters (
and ), { and } are reserved words and must occur at the beginning
of a line or after a ; in order to be recognized.
[[ expression ]]
Evaluates expression and returns a zero exit status when expres-
sion is true. See Conditional Expressions below, for a descrip-
tion of expression.
function varname { list ;} [ redirection ... ]
varname () compound-command [ redirection ... ]
Define a function which is referenced by varname. A function
whose varname contains a . is called a discipline function and
the portion of the varname preceding the last . must refer to an
existing variable. The body of the function is the list of com-
mands between { and }. A function defined with the function var-
name syntax can also be used as an argument to the . special
built-in command to get the equivalent behavior as if the var-
name() syntax were used to define it. (See Functions below.)
namespace identifier { list ;}
Defines or uses the name space identifier and runs the commands
in list in this name space. (See Name Spaces below.)
time [ pipeline ]
If pipeline is omitted the user and system time for the current
shell and completed child processes is printed on standard error.
Otherwise, pipeline is executed and the elapsed time as well as
the user and system time are printed on standard error. The
TIMEFORMAT variable may be set to a format string that specifies
how the timing information should be displayed. See Shell Vari-
ables below for a description of the TIMEFORMAT variable.
The following reserved words are recognized as reserved only when they
are the first word of a command and are not quoted:
if then else elif fi case esac for while until do done { } function se-
lect time [[ ]] !
Variable Assignments.
One or more variable assignments can start a simple command or can be
arguments to the typeset, enum, export, or readonly special built-in
commands as well as to other declaration commands created as types. The
syntax for an assignment is of the form:
varname=word
varname[word]=word
No space is permitted between varname and the = or between = and
word.
varname=(assign_list)
No space is permitted between varname and the =. The variable
varname is unset before the assignment. An assign_list can be
one of the following:
word ...
Indexed array assignment.
[word]=word ...
Associative array assignment. If preceded by
typeset -a this will create an indexed array in-
stead.
assignment ...
Compound variable assignment. This creates a com-
pound variable varname with subvariables of the
form varname.name, where name is the name portion
of assignment. The value of varname will contain
all the assignment elements. Additional assign-
ments made to subvariables of varname will also be
displayed as part of the value of varname. If no
assignments are specified, varname will be a com-
pound variable allowing subsequence child elements
to be defined.
typeset [options] assignment ...
Nested variable assignment. Multiple assignments
can be specified by separating each of them with a
;. The previous value is unset before the assign-
ment. Other declaration commands such as read-
only, enum, and other declaration commands can be
used in place of typeset.
. filename
Include the assignment commands contained in file-
name.
In addition, a += can be used in place of the = to signify adding to or
appending to the previous value. When += is applied to an arithmetic
type, word is evaluated as an arithmetic expression and added to the
current value. When applied to a string variable, the value defined by
word is appended to the value. For compound assignments, the previous
value is not unset and the new values are appended to the current ones
provided that the types are compatible.
The right hand side of a variable assignment undergoes all the expansion
listed below except word splitting, brace expansion, and pathname expan-
sion. When the left hand side is an assignment is a compound variable
and the right hand is the name of a compound variable, the compound
variable on the right will be copied or appended to the compound vari-
able on the left.
Comments.
A word beginning with # causes that word and all the following charac-
ters up to a new-line to be ignored.
Aliasing.
The first word of each command is replaced by the text of an alias if an
alias for this word has been defined. An alias name consists of any
number of characters excluding metacharacters, quoting characters, file
expansion characters, parameter expansion and command substitution char-
acters, the characters / and =. The replacement string can contain any
valid shell script including the metacharacters listed above. The first
word of each command in the replaced text, other than any that are in
the process of being replaced, will be tested for aliases. If the last
character of the alias value is a blank then the word following the
alias will also be checked for alias substitution. Aliases can be used
to redefine built-in commands but cannot be used to redefine the re-
served words listed above. Aliases can be created and listed with the
alias command and can be removed with the unalias command.
Aliasing is performed when scripts are read, not while they are exe-
cuted. Therefore, for an alias to take effect, the alias definition
command has to be executed before the command which references the alias
is read.
The following aliases are automatically preset when the shell is invoked
as an interactive shell. Preset aliases can be unset or redefined.
history=′hist -l′
r=′hist -s′
Tilde Expansion.
After alias substitution is performed, each word is checked to see if it
begins with an unquoted ∼. For tilde expansion, word also refers to the
word portion of parameter expansion (see Parameter Expansion below). If
a word is preceded by a tilde, then it is checked up to a / to see if it
matches a user name in the password database (see getpwname(3)). If a
match is found, the ∼ and the matched login name are replaced by the lo-
gin directory of the matched user. If no match is found, the original
text is left unchanged. A ∼ by itself, or in front of a /, is replaced
by $HOME, unless the HOME variable is unset, in which case the current
user's home directory as configured in the operating system is used. A
∼ followed by a + or - is replaced by $PWD or $OLDPWD respectively.
In addition, when expanding a variable assignment (see Variable Assign-
ments above), tilde expansion is attempted when the value of the assign-
ment begins with a ∼, and when a ∼ appears after a :. A : also termi-
nates a user name following a ∼.
The tilde expansion mechanism may be extended or modified by defining
one of the discipline functions .sh.tilde.set or .sh.tilde.get (see
Functions and Discipline Functions below). If either exists, then upon
encountering a tilde word to expand, that function is called with the
tilde word assigned to either .sh.value (for the .sh.tilde.set function)
or .sh.tilde (for the .sh.tilde.get function). Performing tilde expan-
sion within a discipline function will not recursively call that func-
tion, but default tilde expansion remains active, so literal tildes
should still be quoted where required. Either function may assign a re-
placement string to .sh.value. If this value is non-empty and does not
start with a ∼, it replaces the default tilde expansion when the func-
tion terminates. Otherwise, the tilde expansion is left unchanged.
Subshells.
A subshell is a separate execution environment that is a complete dupli-
cate of the current shell environment, except for two things: all traps
are reset to default except those for signals that are being ignored,
and subshells cannot be interactive (i.e., they have no command prompt).
Changes made within a subshell do not affect the parent environment and
are lost when the subshell exits.
Particular care should be taken not to confuse a subshell with a newly
invoked shell that is merely a child process of the current shell, and
which (unlike a subshell) starts from scratch in terms of variables and
functions and may be interactive. Beware of shell tutorials on the In-
ternet that confuse these.
Subshells cannot be created or invoked using any command. Instead, the
following are automatically run in a subshell:
• any command or group of commands enclosed in parentheses;
• command substitutions of the first and third form (see Com-
mand Substitution below);
• process substitutions (see Process Substitution below);
• all elements of a pipeline except the last;
• any command executed asynchronously (i.e., in a background
process).
Creating processes is expensive, so as a performance optimization, a
subshell of a non-interactive shell may share the process of its parent
environment. Such a subshell is known as a virtual subshell. Subshells
are virtual unless or until something (such as asynchronous execution,
or an attempt to set a process limit using the ulimit built-in command,
or other implementation- or system-defined requirements) makes it neces-
sary to fork(2) it into a separate process. Barring any bugs in the
shell, virtual subshells should be indistinguishable from real subshells
except by their execution speed and their process ID. See the descrip-
tion of the .sh.pid variable below for more information.
Command Substitution.
The standard output from a command list enclosed in parentheses preceded
by a dollar sign ( $(list) ), or in a brace group preceded by a dollar
sign ( ${ list;} ), or in a pair of grave accents (``) may be used as
part or all of a word; trailing new-lines are removed. In the second
case, the { and } are treated as a reserved words so that { must be fol-
lowed by a blank and } must appear at the beginning of the line or fol-
low a ;. In the third (obsolete) form, the string between the quotes is
processed for special quoting characters before the command is executed
(see Quoting below). The command substitution $(cat file) can be re-
placed by the equivalent but faster $(<file). The command substitution
$(n<#) will expand to the current byte offset for file descriptor n.
Except for the second form, the command list is run in a subshell so
that no side effects are possible. For the second form, the final }
will be recognized as a reserved word after any token.
Arithmetic Expansion.
An arithmetic expression enclosed in double parentheses preceded by a
dollar sign ( $(()) ) is replaced by the value of the arithmetic expres-
sion within the double parentheses.
Process Substitution.
Each command argument of the form <(list) or >(list) will run process
list asynchronously connected to some file in /dev/fd if this directory
exists, or else a fifo in a temporary directory. The name of this file
will become the argument to the command. If the form with > is selected
then writing on this file will provide input for list. If < is used,
then the file passed as an argument will contain the output of the list
process. For example,
paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1)
>(process2)
cuts fields 1 and 3 from the files file1 and file2 respectively, pastes
the results together, and sends it to the processes process1 and
process2, as well as putting it onto the standard output. Note that the
file, which is passed as an argument to the command, is a UNIX pipe(2)
so programs that expect to lseek(2) on the file will not work.
Process substitution of the form <(list) can also be used with the <
redirection operator which causes the output of list to be standard in-
put or the input for whatever file descriptor is specified.
Parameter Expansion.
A parameter is a variable, one or more digits, or any of the characters
*, @, #, ?, -, $, and !. A variable is denoted by a vname. To create a
variable whose vname contains a ., a variable whose vname consists of
everything before the last . must already exist. A variable has a value
and zero or more attributes. Variables can be assigned values and at-
tributes by using the typeset special built-in command. The attributes
supported by the shell are described later with the typeset special
built-in command.
The shell supports both indexed and associative arrays. An element of
an array variable is referenced by a subscript. A subscript for an in-
dexed array is denoted by an arithmetic expression (see Arithmetic Eval-
uation below) between a [ and a ]. To assign values to an indexed ar-
ray, use vname=(value ...) or set -A vname value ... . The value of
all non-negative subscripts must be in the range of 0 through 4,194,303.
A negative subscript is treated as an offset from the maximum current
index +1 so that -1 refers to the last element. Indexed arrays can be
declared with the -a option to typeset. Indexed arrays need not be de-
clared. Any reference to a variable with a valid subscript is legal and
an array will be created if necessary.
An associative array is created with the -A option to typeset. A sub-
script for an associative array is denoted by a string enclosed between
[ and ].
Referencing any array without a subscript is equivalent to referencing
the array with subscript 0.
The value of a variable may be assigned by writing:
vname=value [ vname=value ] ...
or
vname[subscript]=value [ vname[subscript]=value ] ...
Note that no space is allowed before or after the =.
Attributes assigned by the typeset special built-in command apply to all
elements of the array. An array element can be a simple variable, a
compound variable or an array variable. An element of an indexed array
can be either an indexed array or an associative array. An element of
an associative array can also be either. To refer to an array element
that is part of an array element, concatenate the subscript in brackets.
For example, to refer to the foobar element of an associative array that
is defined as the third element of the indexed array, use
${vname[3][foobar]}
A nameref is a variable that is a reference to another variable. A
nameref is created with the -n attribute of typeset or with the equiva-
lent nameref command. The value of the variable at the time of that
command becomes the variable that will be referenced whenever the
nameref variable is used. The name of a nameref cannot contain a ..
When a variable or function name contains a ., and the portion of the
name up to the first . matches the name of a nameref, the variable re-
ferred to is obtained by replacing the nameref portion with the name of
the variable referenced by the nameref. If a nameref is used as the in-
dex of a for loop, a name reference is established for each item in the
list.
A nameref provides a convenient way to refer to the variable inside a
function whose name is passed as an argument to a function. For exam-
ple, if the name of a variable is passed as the first argument to a
function, the command typeset -n var=$1 (a.k.a. nameref var=$1) inside
the function causes references and assignments to var to be references
and assignments to the variable whose name has been passed to the func-
tion. Note that, for this to work, the positional parameter must be as-
signed directly to the nameref as part of the declaration command, as in
the example above; only that idiom can allow one function to access a
local variable of another. For instance, typeset -n var; var=$1 won't
cross that barrier, nor will typeset foo=$1; typeset -n var=foo.
If any of the floating point attributes, -E, -F, or -X, or the integer
attribute, -i, is set for vname, then the value is subject to arithmetic
evaluation as described below.
Positional parameters, parameters denoted by a number, may be assigned
values with the set special built-in command. Parameter $0 is set from
argument zero when the shell is invoked.
The character $ is used to introduce substitutable parameters.
${parameter}
The shell reads all the characters from ${ to the matching } as
part of the same word even if it contains braces or metacharac-
ters. The value, if any, of the parameter is substituted. The
braces are required when parameter is followed by a letter,
digit, or underscore that is not to be interpreted as part of its
name, when the variable name contains a .. The braces are also
required when a variable is subscripted unless it is part of an
Arithmetic Expression or a Conditional Expression. If parameter
is one or more digits then it is a positional parameter. A posi-
tional parameter of more than one digit must be enclosed in
braces. If parameter is * or @, then all the positional parame-
ters, starting with $1, are substituted (separated by a field
separator character). If an array vname with last subscript * @,
or for indexed arrays of the form sub1 .. sub2. is used, then
the value for each of the elements between sub1 and sub2 inclu-
sive (or all elements for * and @) is substituted, separated by
the first character of the value of IFS.
${#parameter}
If parameter is * or @, the number of positional parameters is
substituted. Otherwise, the length of the value of the parameter
is substituted.
${#vname[*]}
${#vname[@]}
The number of elements in the array vname is substituted.
${@vname}
Expands to the type name (see Type Variables below) or attrib-
utes of the variable referred to by vname.
${!vname}
Expands to the name of the variable referred to by vname. This
will be vname except when vname is a name reference.
${!vname[subscript]}
Expands to name of the subscript unless subscript is *, @. or of
the form sub1 .. sub2. When subscript is *, the list of array
subscripts for vname is generated. For a variable that is not an
array, the value is 0 if the variable is set. Otherwise it is
the empty string. When subscript is @, same as above, except
that when used in double quotes, each array subscript yields a
separate argument. When subscript is of the form sub1 .. sub2
it expands to the list of subscripts between sub1 and sub2 inclu-
sive using the same quoting rules as @.
${!prefix@}
${!prefix*}
These both expand to the names of the variables whose names begin
with prefix. The expansions otherwise work like $@ and $*, re-
spectively (see under Quoting below).
${parameter:-word}
If parameter is set and has a non-empty value, then substitute
its value; otherwise substitute word.
${parameter:=word}
If parameter is not set or has the empty string value, then set
it to word; the value of the parameter is then substituted. Po-
sitional parameters may not be assigned to in this way.
${parameter:?word}
If parameter is set and has a non-empty value, then substitute
its value; otherwise, print word and exit from the shell (if not
interactive). If word is omitted then a standard message is
printed.
${parameter:+word}
If parameter is set and has a non-empty value then substitute
word; otherwise substitute the empty string.
In the above, word is not evaluated unless it is to be used as the sub-
stituted string, so that, in the following example, pwd is executed only
if d is not set or has the empty string value:
print ${d:-$(pwd)}
If the colon (:) is omitted from the above expressions, then the shell
only checks whether parameter is set or not.
${parameter:offset:length}
${parameter:offset}
Expands to the portion of the value of parameter starting at the
character (counting from 0) determined by expanding offset as an
arithmetic expression and consisting of the number of characters
determined by the arithmetic expression defined by length. In
the second form, the remainder of the value is used. If A nega-
tive offset counts backwards from the end of parameter. Note
that one or more blanks is required in front of a minus sign to
prevent the shell from interpreting the operator as :-. If para-
meter is * or @, or is an array name indexed by * or @, then off-
set and length refer to the array index and number of elements
respectively. A negative offset is taken relative to one greater
than the highest subscript for indexed arrays. The order for as-
sociative arrays is unspecified.
${parameter#pattern}
${parameter##pattern}
If the shell pattern matches the beginning of the value of para-
meter, then the value of this expansion is the value of the para-
meter with the matched portion deleted; otherwise the value of
this parameter is substituted. In the first form the smallest
matching pattern is deleted and in the second form the largest
matching pattern is deleted. When parameter is @, *, or an array
variable with subscript @ or *, the substring operation is ap-
plied to each element in turn.
${parameter%pattern}
${parameter%%pattern}
If the shell pattern matches the end of the value of parameter,
then the value of this expansion is the value of the parameter
with the matched part deleted; otherwise substitute the value of
parameter. In the first form the smallest matching pattern is
deleted and in the second form the largest matching pattern is
deleted. When parameter is @, *, or an array variable with sub-
script @ or *, the substring operation is applied to each element
in turn.
${parameter/pattern/string}
${parameter//pattern/string}
${parameter/#pattern/string}
${parameter/%pattern/string}
Expands parameter and replaces the longest match of pattern with
the given string. Each occurrence of \n in string is replaced by
the portion of parameter that matches the n-th subpattern. In
the first form, only the first occurrence of pattern is replaced.
In the second form, each match for pattern is replaced by the
given string. The third form restricts the pattern match to the
beginning of the string while the fourth form restricts the pat-
tern match to the end of the string. In the first and second
forms, an empty pattern never matches. In the third and fourth
forms, an empty pattern matches the beginning or the end of the
string, respectively. When string is empty, the pattern will be
deleted and the / in front of string may be omitted. When para-
meter is @, *, or an array variable with subscript @ or *, the
substitution operation is applied to each element in turn. In
this case, the string portion of word will be re-evaluated for
each element.
Shell Variables.
The following parameters are automatically set by the shell:
# The number of positional parameters in decimal.
- Options supplied to the shell on invocation or by the set
command.
? The exit status returned by the last executed command. Its
meaning depends on the command or function that defines
it, but there are conventions that other commands often
depend on: zero typically means 'success' or 'true', one
typically means 'non-success' or 'false', and a value
greater than one typically indicates some kind of error.
Only the 8 least significant bits of $? (values 0 to 255)
are preserved when the exit status is passed on to a par-
ent process, but within the same (sub)shell environment,
it is a signed integer value with a range of possible val-
ues as shown by the commands getconf INT_MIN and getconf
INT_MAX. Shell functions that run in the current environ-
ment may return status values in this range.
$ The process ID of the main shell process. Note that this
value will not change in a subshell, even if the subshell
runs in a different process. See also .sh.pid.
_ Initially, the value of _ is an absolute pathname of the
shell or script being executed as passed in the environ-
ment. Subsequently it is assigned the last argument of
the previous command. This parameter is not set for com-
mands which are asynchronous. This parameter is also used
to hold the name of the matching MAIL file when checking
for mail. While defining a compound variable or a type, _
is initialized as a reference to the compound variable or
type. When a discipline function is invoked, _ is ini-
tialized as a reference to the variable associated with
the call to this function. Finally when _ is used as the
name of the first variable of a type definition, the new
type is derived from the type of the first variable. (See
Type Variables below.)
! The process ID of the last background command invoked or
the most recent job put in the background with the bg
built-in command.
.sh.command
When processing a DEBUG trap, this variable contains the
current command line that is about to run. The value is
in the same format as the output generated by the xtrace
option (minus the preceding PS4 prompt).
.sh.edchar
This variable contains the value of the keyboard character
(or sequence of characters if the first character is an
ESC, ASCII 033) that has been entered when processing a
KEYBD trap (see Key Bindings below). If the value is
changed as part of the trap action, then the new value re-
places the key (or key sequence) that caused the trap.
.sh.edcol
The character position of the cursor at the time of the
most recent KEYBD trap.
.sh.edmode
Upon executing a KEYBD trap action, the value of this
variable is set to the ESC control character if the shell
is in vi input mode (See Vi Editing Mode below), or to
the empty string value otherwise.
.sh.edtext
The characters in the input buffer at the time of the most
recent KEYBD trap. The variable is unset when not pro-
cessing a KEYBD trap.
.sh.file
The pathname of the file that contains the current com-
mand.
.sh.fun
The name of the current function that is being executed.
.sh.level
Set to the current call depth of functions and dot
scripts. Normally, this variable is read-only, but while
executing a DEBUG trap, its value may be changed to switch
the current function scope to that of the specified level
for the duration of the trap run, making it possible to
access a parent scope for debugging purposes. When trap
execution ends, the variable and the scope are restored.
It is an error to assign a value lower than 0 (the global
scope) or higher than the current call depth.
.sh.lineno
Set during a DEBUG trap to the line number for the caller
of each function.
.sh.match
Whenever a match is found in a pattern matching operation
using either the [[ compound command (see Conditional Ex-
pressions below) or the expansions ${parameter#pattern},
${parameter%pattern}, ${parameter/pattern/string}, or one
of their variants (see Parameter Expansion above), the
match and its subpattern matches are stored in this in-
dexed array, overwriting its previous values. The 0-th
element stores the complete match and the i-th element
stores the i-th submatch. For //, the array is two-dimen-
sional, with the first subscript indicating the most re-
cent match and subpattern match, and the second subscript
indicating which match with 0 representing the first
match. If no match is found, .sh.match is not reset or
modified. Note that even matching operations performed on
the .sh.match variable itself will overwrite it upon find-
ing a match.
.sh.math
Used for defining arithmetic functions (see Arithmetic
Evaluation below) and stores the list of user defined
arithmetic functions.
.sh.name
Set to the name of the variable at the time that a disci-
pline function is invoked.
.sh.subscript
Set to the name subscript of the variable at the time that
a discipline function is invoked.
.sh.subshell
The current depth for subshells and command substitution.
.sh.pid
Set to the process ID of the current shell process. Un-
like $$, this is updated in a subshell when it forks into
a new process. Note that a virtual subshell may have to
fork mid-execution due to various system- and implementa-
tion-dependent requirements, so the value should not be
counted on to remain the same from one command to the
next. If a persistent process ID is required for a sub-
shell, it must be ensured it is running in its own process
first. Any attempt to set a process limit using the
ulimit built-in command, such as ulimit -t unlimited
2>/dev/null, is a reliable way to make a subshell fork if
it hasn't already.
.sh.ppid
Set to the process ID of the parent of the current shell
process. Unlike $PPID, this is updated in a subshell when
it forks into a new process. The same note as for .sh.pid
applies.
.sh.value
Set to the value of the variable at the time that the set
or append discipline function is invoked. When a user de-
fined arithmetic function is invoked, the value of
.sh.value is saved and .sh.value is set to long double
precision floating point. .sh.value is restored when the
function returns.
.sh.version
Set to a value that identifies the version of this shell.
COLUMNS
Width of the terminal window in character positions. Up-
dated automatically at initialization and on receiving a
SIGWINCH signal. The shell uses the value to define the
width of the edit window for the shell edit modes and for
printing select lists.
KSH_VERSION
A name reference to .sh.version.
LINENO The current line number within the script or function be-
ing executed.
LINES Height of the terminal window in lines. Updated automati-
cally at initialization and on receiving a SIGWINCH sig-
nal. The shell uses the value to determine the column
length for printing select lists: they are printed verti-
cally until about two thirds of LINES lines are filled.
OLDPWD The previous working directory set by the cd command.
OPTARG The value of the last option argument processed by the
getopts built-in command.
OPTIND The index of the last option argument processed by the
getopts built-in command.
PPID The process ID of the parent of the main shell process.
Note that this value will not change in a subshell, even
if the subshell runs in a different process. See also
.sh.ppid.
PWD The present working directory set by the cd command.
RANDOM Each time this variable is referenced, a pseudorandom in-
teger is generated, uniformly distributed between 0 and
32767 (the 16-bit unsigned integer range) except that the
same number is never repeated twice in a row. The se-
quence of pseudorandom numbers is reproducible and can be
initialized to a fixed starting point by assigning a nu-
meric seed value to RANDOM. Each time a new shell or sub-
shell environment is entered (see Subshells above), the
sequence is automatically reset to a different point.
REPLY This variable is set by the select statement and by the
read built-in command when no arguments are supplied.
SECONDS
Each time this variable is referenced, the number of sec-
onds since shell invocation is returned. If this variable
is assigned a value, then the value returned upon refer-
ence will be the value that was assigned plus the number
of seconds since the assignment.
SHLVL An integer variable that is incremented and exported each
time the shell is invoked. If SHLVL is not in the envi-
ronment when the shell is invoked, it is set to 1.
The following variables are used by the shell:
CDPATH The search path for the cd command.
EDITOR If the VISUAL variable is not set, the value of this vari-
able will be checked for certain patterns and the corre-
sponding editing option will be turned on as described
with VISUAL below.
ENV If this variable is set, then parameter expansion, command
substitution, and arithmetic expansion are performed on
the value to generate the pathname of the script that will
be executed when the shell is invoked interactively (see
Invocation below). This file is typically used for alias
and function definitions. The default value is
$HOME/.kshrc. On systems that support a system wide
/etc/ksh.kshrc initialization file, if the filename gener-
ated by the expansion of ENV begins with /./ or ././ the
system wide initialization file will not be executed.
FCEDIT Obsolete name for the default editor name for the hist
command. FCEDIT is not used when HISTEDIT is set.
FIGNORE
A pattern that defines the set of filenames that will be
ignored when performing filename matching.
FPATH The search path for function definitions. The directories
in this path are searched for a file with the same name as
the function or command when a function with the -u at-
tribute is referenced and when a command is not found. If
an executable file with the name of that command is found,
then it is read and executed in the current environment.
Unlike PATH, the current directory must be represented ex-
plicitly by . rather than by adjacent : characters or a
beginning or ending :.
histchars
This variable can be used to specify up to three ASCII
characters that control history expansion (see History Ex-
pansion below). The first (default: !) signals the start
of a history expansion. The second (default: ^) is used
for short-form substitutions. The third (default: #),
when found as the first character of a word, causes his-
tory expansion to be skipped for the rest of the words on
the line. Multi-byte characters (e.g. UTF-8) are not sup-
ported and produce undefined results.
HISTCMD
Number of the current command in the history file.
HISTEDIT
Name for the default editor name for the hist command.
HISTFILE
If this variable is set when the shell is invoked, then
the value is the pathname of the file that will be used to
store the command history (see Command Re-entry below).
HISTSIZE
If this variable is set when the shell is invoked, then
the number of previously entered commands that are acces-
sible by this shell will be greater than or equal to this
number. The default is 512.
HOME The default argument (home directory) for the cd command.
IFS Internal field separators, normally space, tab, and new-
line that are used to separate the results of command sub-
stitution or parameter expansion and to separate fields
with the built-in command read. The first character of
the IFS variable is used to separate arguments for the
"$*" expansion (see Quoting below). Each single occur-
rence of an IFS character in the string to be split that
is not in the isspace character class, and any adjacent
characters in IFS that are in the isspace character class,
delimit a field. One or more characters in IFS that be-
long to the isspace character class delimit a field. In
addition, if the same isspace character appears consecu-
tively inside IFS and the posix shell option is not on,
this character is treated as if it were not in the isspace
class - for example, if IFS consists of two tab charac-
ters, then two adjacent tab characters delimit an empty
field.
JOBMAX This variable defines the maximum number running back-
ground jobs that can run at a time. When this limit is
reached, the shell will wait for a job to complete before
starting a new job.
LANG This variable determines the locale category for any cate-
gory not specifically selected with a variable starting
with LC_ or LANG.
LC_ALL This variable overrides the value of the LANG variable and
any other LC_ variable.
LC_COLLATE
This variable determines the locale category for character
collation information.
LC_CTYPE
This variable determines the locale category for character
handling functions. It determines the character classes
for pattern matching (see Pathname Expansion below).
LC_NUMERIC
This variable determines the locale category for the deci-
mal point character.
MAIL If this variable is set to the name of a mail file and the
MAILPATH variable is not set, then the shell informs the
user of arrival of mail in the specified file.
MAILCHECK
This variable specifies how often (in seconds) the shell
will check for changes in the modification time of any of
the files specified by the MAILPATH or MAIL variables.
The default value is 600 seconds. When the time has
elapsed the shell will check before issuing the next
prompt.
MAILPATH
A colon ( : ) separated list of file names. If this vari-
able is set, then the shell informs the user of any modi-
fications to the specified files that have occurred within
the last MAILCHECK seconds. Each file name can be fol-
lowed by a ? and a message that will be printed. The
message will undergo parameter expansion, command substi-
tution, and arithmetic expansion with the variable $_ de-
fined as the name of the file that has changed. The de-
fault message is you have mail in $_.
PATH The search path for commands (see Execution below). The
user may not change PATH if executing under rksh (except
in .profile).
PS1 Every time a new command line is started on an interactive
shell, the value of this variable is expanded to resolve
backslash escaping, parameter expansion, command substitu-
tion, and arithmetic expansion. The result defines the
primary prompt string for that command line. The default
is ``$ ''. The character ! in the primary prompt string
is replaced by the command number (see Command Re-entry
below). Two successive occurrences of ! will produce a
single ! when the prompt string is printed. Note that
any terminal escape sequences used in the PS1 prompt thus
need every instance of ! in them to be changed to !!.
PS2 Secondary prompt string, by default ``> ''.
PS3 Selection prompt string used within a select loop, by de-
fault ``#? ''.
PS4 The value of this variable is expanded for parameter eval-
uation, command substitution, and arithmetic expansion and
precedes each line of an execution trace. By default, PS4
is ``+ ''. In addition when PS4 is unset, the execution
trace prompt is also ``+ ''.
SHELL The pathname of the shell is kept in the environment. At
invocation, if the basename of this variable is rsh, rksh,
or krsh, then the shell becomes restricted.
TIMEFORMAT
The value of this parameter is used as a format string
specifying how the timing information for pipelines pre-
fixed with the time reserved word should be displayed.
The % character introduces a format sequence that is ex-
panded to a time value or other information. The format
sequences and their meanings are as follows.
%% A literal %.
%[p][l]R The elapsed time in seconds.
%[p][l]U The number of CPU seconds spent in user mode.
%[p][l]S The number of CPU seconds spent in system mode.
%P The CPU percentage, computed as (U + S) / R.
The brackets denote optional portions. The optional p is
a digit specifying the precision, the number of fractional
digits after a decimal point. A value of 0 causes no dec-
imal point or fraction to be output. At most three places
after the decimal point can be displayed; values of p
greater than 3 are treated as 3. If p is not specified,
the value 3 is used.
The optional l specifies a longer format, including hours
if greater than zero, minutes, and seconds of the form
HHhMMmSS.FFs. The value of p determines whether or not
the fraction is included. Seconds are zero-padded unless
the posix shell option is on.
All other characters are output without change and a
trailing newline is added. If the variable is unset, the
default value, $'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS', is
used. If the value is empty, no timing information is
displayed.
TMOUT Terminal read timeout. If set to a value greater than
zero, the read built-in command and the select compound
command time out after TMOUT seconds when input is from a
terminal. An interactive shell will issue a warning and
allow for an extra 60 second timeout grace period before
terminating if a line is not entered within the prescribed
number of seconds while reading from a terminal. (Note
that the shell can be compiled with a maximum bound for
this value which cannot be exceeded.)
VISUAL The value of this variable is scanned when the shell is
invoked and whenever its value is changed; if it is found
to match certain patterns, the corresponding line editor
(see In-line Editing Options below) is activated. If it
matches the pattern *[Vv][Ii]*, the vi option is turned
on; else if it matches the pattern *gmacs*, the gmacs op-
tion is turned on; else if it matches the pattern *macs*,
the emacs option is turned on. If none of the patterns
match, emacs is turned on by default upon initializing an
interactive shell. If the value is changed by assignment
and none of the patterns match, no options are changed.
The value of VISUAL overrides the value of EDITOR.
The shell gives default values to PATH, PS1, PS2, PS3, PS4, MAILCHECK,
FCEDIT, TMOUT and IFS, while HOME, SHELL, ENV, histchars, and MAIL are
not set at all by the shell (although HOME is set by login(1)). On some
systems MAIL and SHELL are also set by login(1).
Field Splitting.
After parameter expansion and command substitution, the results of sub-
stitutions are scanned for the field separator characters (those found
in IFS) and split into distinct fields where such characters are found.
Explicit empty fields ("" or ′′) are retained. Implicit empty fields
(those resulting from parameters that are unset or have empty string
values or from command substitutions yielding the empty string, and that
are not quoted with "") are removed.
Brace Expansion.
If the braceexpand (-B) option is set then each word, as well as any
fields resulting from field splitting (see above), are checked to see if
they contain one or more of the brace patterns {*,*}, {l1..l2},
{n1..n2}, {n1..n2%fmt}, {n1..n2..n3}, or {n1..n2..n3%fmt}, where * rep-
resents any character, l1,l2 are letters and n1,n2,n3 are signed numbers
and fmt is a format specified as used by printf. In each case, fields
are created by prepending the characters before the { and appending the
characters after the } to each of the strings generated by the charac-
ters between the { and }. The resulting fields are checked to see if
they have any brace patterns.
In the first form, a field is created for each string between { and ,,
between , and ,, and between , and }. The string represented by * can
contain embedded matching { and } without quoting. Otherwise, each {
and } with * must be quoted.
In the second form, l1 and l2 must both be either upper case or both be
lower case characters in the C locale. In this case a field is created
for each character from l1 through l2.
In the remaining forms, a field is created for each number starting at
n1 and continuing until it reaches n2 incrementing n1 by n3. The values
of n1, n2 and n3 are limited to the standard integer range as output by
getconf INT_MIN and getconf INT_MAX; the behavior is undefined if this
range is exceeded. The cases where n3 is not specified behave as if n3
where 1 if n1<=n2 and -1 otherwise. If forms which specify %fmt any
format flags, widths and precisions can be specified and fmt can end in
any of the specifiers cdiouxX. For example, {a,z}{1..5..3%02d}{b..c}x
expands to the 8 fields, a01bx, a01cx, a04bx, a04cx, z01bx, z01cx, z04bx
and z04cx.
Pathname Expansion.
This is also known as globbing or sometimes filename generation. Path-
name expansion is disabled if the -f a.k.a. --noglob shell option is
on. Otherwise, if certain special characters are found in a word or in
a field resulting from field splitting (see above), then the word or
field is regarded as a pattern. Each literal word is scanned for the
characters *, ?, [, and (, but fields resulting from field splitting are
scanned only for the characters *, ?, and [ for compatibility reasons
(in which case the ( character is not special and any pattern syntax de-
scribed below that involves parentheses does not apply).
Each file name component that contains a recognized pattern character is
replaced with a lexicographically sorted set of names that matches the
pattern from that directory. If no file name is found that matches the
pattern, then that component of the filename is left unchanged unless
the pattern is prefixed with ∼(N), in which case it is removed as de-
scribed below. The special traversal names . and .. are never
matched. If FIGNORE is set, then each file name component that matches
the pattern defined by the value of FIGNORE is ignored when generating
the matching filenames. If FIGNORE is not set, the character . at the
start of each file name component will be ignored unless the first char-
acter of the pattern corresponding to this component is the character .
itself. Note that, for uses of pattern matching other than pathname ex-
pansion, the / and . are not treated specially.
* Matches any string, including the empty string. When used
for filename expansion, if the globstar option is on, an
isolated pattern of two adjacent *s will match all files
and zero or more directories and subdirectories. If fol-
lowed by a / then only directories and subdirectories will
match.
? Matches any single character.
[...] Matches any one of the enclosed characters. A pair of
characters separated by - matches any character lexically
between the pair, inclusive. If the first character fol-
lowing the opening [ is a ! or ^, then any character not
enclosed is matched. A - can be included in the character
set by putting it as the first or last character.
Within [ and ], character classes can be specified with
the syntax [:class:], where class is one of the following
classes defined in the ANSI C standard (note that word is
equivalent to alnum plus the character _):
alnum alpha blank cntrl digit graph lower print punct
space upper word xdigit
Within [ and ], an equivalence class can be specified with
the syntax [=c=] which matches all characters with the
same primary collation weight (as defined by the current
locale) as the character c. Within [ and ], [.symbol.]
matches the collating symbol symbol.
A pattern-list is a list of one or more patterns separated from each
other with a & or |. A & signifies that all patterns must be matched
whereas | requires that only one pattern be matched. Composite patterns
can be formed with one or more of the following subpatterns:
?(pattern-list)
Optionally matches any one of the given patterns.
*(pattern-list)
Matches zero or more occurrences of the given patterns.
+(pattern-list)
Matches one or more occurrences of the given patterns.
{n}(pattern-list)
Matches n occurrences of the given patterns.
{m,n}(pattern-list)
Matches from m to n occurrences of the given patterns. If
m is omitted, 0 will be used. If n is omitted, at least m
occurrences will be matched.
@(pattern-list)
Matches exactly one of the given patterns.
!(pattern-list)
Matches anything except one of the given patterns.
By default, each pattern or subpattern will match the longest string
possible consistent with generating the longest overall match. If more
than one match is possible, the one starting closest to the beginning of
the string will be chosen. However, for each of the above compound
patterns, a - can be inserted in front of the ( to cause the shortest
match to the specified pattern-list to be used.
When pattern-list is contained within parentheses, the backslash charac-
ter \ is treated specially even when inside a character class. All
ANSI C character escapes are recognized and match the specified charac-
ter. In addition, the following escape sequences are recognized:
\d Matches any character in the digit class.
\D Matches any character not in the digit class.
\s Matches any character in the space class.
\S Matches any character not in the space class.
\w Matches any character in the word class.
\W Matches any character not in the word class.
A pattern of the form %(pattern-pair(s)) is a subpattern that can be
used to match nested character expressions. Each pattern-pair is a two-
character sequence that cannot contain & or |. The first pattern-pair
specifies the starting and ending characters for the match. Each subse-
quent pattern-pair represents the beginning and ending characters of a
nested group that will be skipped over when counting starting and ending
character matches. The behavior is unspecified when the first character
of a pattern-pair is alphanumeric, except for the following:
D Causes the ending character to terminate the search for
this pattern without finding a match.
E Causes the ending character to be interpreted as an escape
character.
L Causes the ending character to be interpreted as a quote
character, causing all characters to be ignored when look-
ing for a match.
Q Causes the ending character to be interpreted as a quote
character, causing all characters other than any escape
character to be ignored when looking for a match.
Thus, %({}Q"E\), matches characters starting at { until the matching }
is found, not counting any { or } that is inside a double-quoted string
or preceded by the escape character \. Without the {}, this pattern
matches any C language string.
Each subpattern in a composite pattern is numbered, starting at 1, by
the location of the ( within the pattern. The sequence \n, where n is a
single digit and \n comes after the nth subpattern, matches the same
string as the subpattern itself.
Finally, a pattern can contain subpatterns of the form ∼(options:pat-
tern-list), where either options or :pattern-list can be omitted. Un-
like the other compound patterns, these subpatterns are not counted in
the numbered subpatterns. :pattern-list must be omitted for options E,
F, G, N, P, V, and X below. If options is present, it can consist of
one or more of the following:
+ Enable the following options. This is the default.
- Disable the following options.
E The remainder of the pattern uses extended regular expres-
sion syntax like the -E option of the grep(1) command.
F The remainder of the pattern uses the fixed pattern syntax
of the -F option of the grep(1) command.
G The remainder of the pattern uses basic regular expression
syntax like the grep(1) command without options.
K The remainder of the pattern uses shell pattern syntax.
This is the default.
N When it is the first letter and is used with pathname ex-
pansion, and no matches occur, the file pattern expands to
the empty string instead of remaining unexpanded. Other-
wise, it is ignored.
X The remainder of the pattern uses augmented regular ex-
pression syntax like the -X option of the AT&T AST version
of the grep(1) command.
P The remainder of the pattern uses perl(1) regular expres-
sion syntax. Not all perl regular expression syntax is
currently implemented.
V The remainder of the pattern uses System V regular expres-
sion syntax.
i Always treat the match as case-insensitive, regardless of
the globcasedetect shell option.
g File the longest match (greedy). This is the default.
l Left-anchor the pattern. This is the default for K style
patterns.
r Right-anchor the pattern. This is the default for K style
patterns.
If both options and :pattern-list are specified, then the options apply
only to pattern-list. Otherwise, these options remain in effect until
they are disabled by a subsequent ∼(...) or at the end of the subpattern
containing ∼(...).
Quoting.
Each of the metacharacters listed earlier (see Definitions above) has a
special meaning to the shell and causes termination of a word unless
quoted. A character may be quoted (i.e., made to stand for itself) by
preceding it with a \. The pair \new-line is removed. All characters
enclosed between a pair of single quote marks (′′) that is not preceded
by a $ are quoted. A single quote cannot appear within the single
quotes. A single quoted string preceded by an unquoted $ is processed
as a C99 string except for the following:
\0 Causes the remainder of the string to be ignored.
\E Equivalent to the escape character (ASCII 033),
\e Equivalent to the escape character (ASCII 033),
\cx Expands to the character control-x.
\C[.name.]
Expands to the collating element name.
Inside double quote marks (""), parameter and command substitution occur
and \ quotes the characters \, `, ", and $. A $ in front of a double
quoted string will be ignored in the "C" or "POSIX" locale, and may
cause the string to be replaced by a locale specific string otherwise.
The meaning of $* and $@ is identical when not quoted or when used as a
variable assignment value or as a file name. However, when used as a
command argument, "$*" is equivalent to "$1d$2d...", where d is the
first character of the IFS variable, whereas "$@" is equivalent to "$1"
"$2" .... Inside grave quote marks (``), \ quotes the characters \, `,
and $. If the grave quotes occur within double quotes, then \ also
quotes the character ".
The special meaning of reserved words or aliases can be removed by quot-
ing any character of the reserved word. The recognition of function
names or built-in command names listed below cannot be altered by quot-
ing them.
Arithmetic Evaluation.
The shell performs arithmetic evaluation for arithmetic expansion, to
evaluate an arithmetic command, to evaluate an indexed array subscript,
and to evaluate arguments to the built-in commands shift and let as well
as arguments to numeric format specifiers given to print -f and printf.
Evaluations are performed using double precision floating point arith-
metic or long double precision floating point for systems that provide
this data type. Floating point constants follow the ANSI C programming
language floating point conventions. The case-insensitive floating
point constants NaN and Inf can be used to represent "not a number" and
infinity respectively, unless the posix shell option is on. Integer
constants follow the ANSI C programming language integer constant con-
ventions although only single byte character constants are recognized
and character casts are not recognized.
In addition, integer constants can be of the form base#n or (for nega-
tive numbers) -base#n, where base is a decimal number between two and
sixty-four representing the arithmetic base, and n is an unsigned inte-
ger in that base. The digits above 9 are represented by the lower case
letters, the upper case letters, @, and _, respectively. For bases less
than or equal to 36, upper and lower case letters can be used inter-
changeably.
An arithmetic expression uses the same syntax, precedence, and associa-
tivity of expression as the C language. All the C language operators
that apply to floating point quantities can be used. In addition, the
operator ** can be used for exponentiation. It has higher precedence
than multiplication and is left associative. In addition, when the
value of an arithmetic variable or subexpression can be represented as a
long integer, all C language integer arithmetic operations can be per-
formed. Variables can be referenced by name within an arithmetic ex-
pression without using the parameter expansion syntax. When a variable
is referenced, its value is evaluated as an arithmetic expression.
Any of the following math library functions that are in the C math li-
brary can be used within an arithmetic expression:
abs acos acosh asin asinh atan atan2 atanh cbrt ceil copysign cos cosh
erf erfc exp exp10 exp2 expm1 fabs fdim finite float floor fma fmax fmin
fmod fpclass fpclassify hypot ilogb int isfinite isgreater is-
greaterequal isinf isinfinite isless islessequal islessgreater isnan is-
normal issubnormal isunordered iszero j0 j1 jn ldexp lgamma log log10
log1p log2 logb nearbyint nextafter nexttoward pow remainder rint round
scalb scalbn signbit sin sinh sqrt tan tanh tgamma trunc y0 y1 yn
In addition, arithmetic functions can be defined as shell functions with
a variant of the function name syntax,
function .sh.math.name ident ... { list ;}
where name is the function name used in the arithmetic expression
and each identifier, ident is a name reference to the long double
precision floating point argument. The value of .sh.value when
the function returns is the value of this function. User defined
functions can take up to 3 arguments and override C math library
functions.
An internal representation of a variable as a double precision floating
point can be specified with the -E [n], -F [n], or -X [n] option of the
typeset special built-in command. The -E option causes the expansion of
the value to be represented using scientific notation when it is ex-
panded. The optional option argument n defines the number of signifi-
cant figures. The -F option causes the expansion to be represented as a
floating decimal number when it is expanded. The -X option causes the
expansion to be represented using the %a format defined by ISO C-99.
The optional option argument n defines the number of places after the
decimal (or radix) point in this case.
An internal integer representation of a variable can be specified with
the -i [n] option of the typeset special built-in command. The optional
option argument n specifies an arithmetic base to be used when expanding
the variable. If you do not specify an arithmetic base, base 10 will be
used.
Arithmetic evaluation is performed on the value of each assignment to a
variable with the -E, -F, -X, or -i attribute. Assigning a floating
point number to a variable whose type is an integer causes the frac-
tional part to be truncated.
Prompting.
When used interactively, the shell prompts with the value of PS1 after
expanding it for parameter expansion, command substitution, and arith-
metic expansion, before reading a command. In addition, each single !
in the prompt is replaced by the command number. A !! is required to
place ! in the prompt. If at any time a new-line is typed and further
input is needed to complete a command, then the secondary prompt (i.e.,
the value of PS2) is issued.
Conditional Expressions.
A conditional expression is used with the [[ compound command to test
attributes of files and to compare strings. Field splitting and path-
name expansion are not performed on the words between [[ and ]]. Each
expression can be constructed from one or more of the following unary or
binary expressions:
string Same as -n string below.
-a file
Same as -e below. This is obsolete.
-b file
True if file exists and is a block special file.
-c file
True if file exists and is a character special file.
-d file
True if file exists and is a directory.
-e file
True if file exists.
-f file
True if file exists and is an ordinary file.
-g file
True if file exists and it has its setgid bit set.
-k file
True if file exists and it has its sticky bit set.
-n string
True if length of string is non-zero.
-o ?option
True if option named option is a valid option name.
-o option
True if option named option is on.
-p file
True if file exists and is a fifo special file or a pipe.
-r file
True if file exists and is readable by current process.
-s file
True if file exists and has size greater than zero.
-t fildes
True if file descriptor number fildes is open and associ-
ated with a terminal device.
-u file
True if file exists and it has its setuid bit set.
-v name
True if variable name is a valid variable name and is set.
-w file
True if file exists and is writable by current process.
-x file
True if file exists and is executable by current process.
If file exists and is a directory, then true if the cur-
rent process has permission to search in the directory.
-z string
True if length of string is zero.
-L file
True if file exists and is a symbolic link.
-h file
True if file exists and is a symbolic link.
-N file
True if file exists and the modification time is greater
than the last access time.
-O file
True if file exists and is owned by the effective user ID
of this process.
-G file
True if file exists and its group matches the effective
group ID of this process.
-R name
True if variable name is a name reference.
-S file
True if file exists and is a socket.
file1 -nt file2
True if file1 exists and file2 does not, or file1 is newer
than file2.
file1 -ot file2
True if file2 exists and file1 does not, or file1 is older
than file2.
file1 -ef file2
True if file1 and file2 exist and refer to the same file.
string == pattern
True if string matches pattern. Any part of pattern can
be quoted to cause it to be matched as a string. With a
successful match to a pattern, the .sh.match array vari-
able will contain the match and subpattern matches.
string = pattern
Same as == above, but is obsolete.
string != pattern
True if string does not match pattern. When the string
matches the pattern the .sh.match array variable will con-
tain the match and subpattern matches.
string =∼ ere
True if string matches the pattern ∼(E)ere where ere is an
extended regular expression.
string1 < string2
True if string1 comes before string2 based on ASCII value
of their characters.
string1 > string2
True if string1 comes after string2 based on ASCII value
of their characters.
The following obsolete arithmetic comparisons are also permitted:
exp1 -eq exp2
True if exp1 is equal to exp2.
exp1 -ne exp2
True if exp1 is not equal to exp2.
exp1 -lt exp2
True if exp1 is less than exp2.
exp1 -gt exp2
True if exp1 is greater than exp2.
exp1 -le exp2
True if exp1 is less than or equal to exp2.
exp1 -ge exp2
True if exp1 is greater than or equal to exp2.
In each of the above expressions, if file is of the form /dev/fd/n,
where n is an integer, then the test is applied to the open file whose
descriptor number is n. The posix shell option disables this special
handling.
A compound expression can be constructed from these primitives by using
any of the following, listed in decreasing order of precedence:
(expression)
True if expression is true. Used to group expressions.
! expression
True if expression is false.
expression1 && expression2
True if expression1 and expression2 are both true.
expression1 || expression2
True if either expression1 or expression2 is true.
Input/Output.
Before a command is executed, its input and output may be redirected us-
ing a special notation interpreted by the shell. The following may ap-
pear anywhere in a simple-command or may precede or follow a command and
are not passed on to the invoked command. Command substitution, parame-
ter expansion, and arithmetic expansion occur before word or digit is
used except as noted below. Pathname expansion occurs only if the shell
is interactive and the pattern matches a single file. Field splitting
is not performed.
In each of the following redirections, if file is of the form
/dev/sctp/host/port, /dev/tcp/host/port, or /dev/udp/host/port, where
host is a hostname or host address, and port is a service given by name
or an integer port number, then the redirection attempts to make a tcp,
sctp or udp connection to the corresponding socket.
No intervening space is allowed between the characters of redirection
operators.
<word Use file word as standard input (file descriptor 0).
>word Use file word as standard output (file descriptor 1). If
the file does not exist then it is created. If the file
exists, and the noclobber option is on, this causes an er-
ror; otherwise, it is truncated to zero length.
>|word Same as >, except that it overrides the noclobber option.
>;word Write output to a temporary file. If the command com-
pletes successfully rename it to word, otherwise, delete
the temporary file. >;word cannot be used with the exec
and redirect built-ins.
>>word Use file word as standard output. If the file exists,
then output is appended to it (by first seeking to the
end-of-file); otherwise, the file is created.
<>word Open file word for reading and writing as standard output.
If the posix option is active, it defaults to standard in-
put instead.
<>;word The same as <>word except that if the command completes
successfully, word is truncated to the offset at command
completion. <>;word cannot be used with the exec and
redirect built-ins.
<<[-]word The shell input is read up to a line that is the same as
word after any quoting has been removed, or to an end-of-
file. No parameter expansion, command substitution,
arithmetic expansion or pathname expansion is performed on
word. The resulting document, called a here-document, be-
comes the standard input. If any character of word is
quoted, then no interpretation is placed upon the charac-
ters of the document; otherwise, parameter expansion, com-
mand substitution, and arithmetic expansion occur, \new-
line is ignored, and \ must be used to quote the charac-
ters \, $, `. If - is appended to <<, then all leading
tabs are stripped from word and from the document. If #
is appended to <<, then leading spaces and tabs will be
stripped off the first line of the document and up to an
equivalent indentation will be stripped from the remaining
lines and from word. A tab stop is assumed to occur at
every 8 columns for the purposes of determining the inden-
tation.
<<<word A short form of here document in which word becomes the
contents of the here-document after any parameter expan-
sion, command substitution, and arithmetic expansion oc-
cur.
<&digit The standard input is duplicated from file descriptor
digit (see dup(2)).
>&digit The standard output is duplicated from file descriptor
digit.
<&digit- The file descriptor given by digit is moved to standard
input.
>&digit- The file descriptor given by digit is moved to standard
output.
<&- The standard input is closed.
>&- The standard output is closed.
<&p The input from the co-process is moved to standard input.
>&p The output to the co-process is moved to standard output.
<#((expr)) Evaluate arithmetic expression expr and position file de-
scriptor 0 to the resulting value bytes from the start of
the file. The variables CUR and EOF evaluate to the cur-
rent offset and end-of-file offset respectively when eval-
uating expr.
>#((offset)) The same as <# except applies to file descriptor 1.
<#pattern Seeks forward to the beginning of the next line containing
pattern.
<##pattern The same as <# except that the portion of the file that is
skipped is copied to standard output.
If one of the above is preceded by a digit, with no intervening space,
then the file descriptor number referred to is that specified by the
digit (instead of the default 0 or 1). If one of the above, other than
>&- and the ># and <# forms, is preceded by {varname} with no interven-
ing space, then a file descriptor number > 9 will be selected by the
shell and stored in the variable varname, so it can be read from or
written to with redirections like <& $varname or >& $varname. If >&- or
the any of the ># and <# forms is preceded by {varname} the value of
varname defines the file descriptor to close or position. For example:
... 2>&1
means file descriptor 2 is to be opened for writing as a duplicate of
file descriptor 1 and
exec {n}<file
means open file named file for reading and store the file descriptor
number in variable n.
A special shorthand redirection operator &>word is available; it is
equivalent to >word 2>&1. It cannot be preceded by any digit or variable
name. This shorthand is disabled if the posix shell option is active.
The order in which redirections are specified is significant. The shell
evaluates each redirection in terms of the (file descriptor, file) asso-
ciation at the time of evaluation. For example:
... 1>fname 2>&1
first associates file descriptor 1 with file fname. It then associates
file descriptor 2 with the file associated with file descriptor 1 (i.e.
fname). If the order of redirections were reversed, file descriptor 2
would be associated with the terminal (assuming file descriptor 1 had
been) and then file descriptor 1 would be associated with file fname.
If a command is followed by & and job control is not active, then the
default standard input for the command is the empty file /dev/null.
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by input/output spec-
ifications.
Environment.
The environment (see environ(7)) is a list of name-value pairs that is
passed to an executed program in the same way as a normal argument list.
The names must be identifiers and the values are character strings. The
shell interacts with the environment in several ways. On invocation,
the shell scans the environment and creates a variable for each name
found, giving it the corresponding value and attributes and marking it
export. Executed commands inherit the environment. If the user modi-
fies the values of these variables or creates new ones, using the export
or typeset -x commands, they become part of the environment. The envi-
ronment seen by any executed command is thus composed of any name-value
pairs originally inherited by the shell, whose values may be modified by
the current shell, plus any additions which must be noted in export or
typeset -x commands.
Exported variables pass their attributes though the environment so that
a newly invoked ksh that is a child or exec'd process of the current
shell will automatically import them, unless the posix shell option is
on. As of ksh 93u+m/1.0, this never includes the readonly attribute.
Passing attributes through the environment is deprecated and this fea-
ture will be removed in ksh 93u+m/1.1.
The environment for any simple-command or function may be augmented by
prefixing it with one or more variable assignments. A variable assign-
ment argument is a word of the form identifier=value. Thus:
TERM=450 cmd args and
(export TERM; TERM=450; cmd args)
are equivalent (as far as the above execution of cmd is concerned except
for special built-in commands listed below - those that are marked with
†).
If the obsolete -k option is set, all variable assignment arguments are
placed in the environment, even if they occur after the command name.
The following first prints a=b c and then c:
echo a=b c
set -k
echo a=b c
This feature is intended for use with scripts written for early versions
of the shell and its use in new scripts is strongly discouraged. It is
likely to disappear someday.
Functions.
For historical reasons, there are two ways to define functions, the
name() syntax and the function name syntax, described in the Commands
section above. Shell functions are read in and stored internally.
Alias names are resolved when the function is read. Functions are exe-
cuted like commands with the arguments passed as positional parameters.
(See Execution below.)
Functions defined by the function name syntax and called by name execute
in the same process as the caller and share all files and present work-
ing directory with the caller. All changes to shell options are local
to the function call. The errexit option is turned off in the func-
tion's scope. The same applies to the xtrace option, unless the func-
trace shell option is set or the function was tagged using typeset -f
-t. The state of all other shell options is inherited from the caller.
Traps caught by the caller are reset to their default action inside the
function. A trap condition that is not caught or ignored by the func-
tion causes the function to terminate and the condition to be passed on
to the caller. A trap on EXIT set inside a function is executed in the
environment of the caller after the function completes. Ordinarily,
variables are shared between the calling program and the function. How-
ever, the typeset special built-in command used within a function de-
fines local variables whose scope includes the current function. They
can be passed to functions that they call in the variable assignment
list that precedes the call or as arguments passed as name references.
Errors within functions return control to the caller.
Functions defined with the name() syntax and functions defined with the
function name syntax that are invoked with the . special built-in are
executed in the caller's environment and share all variables, options
and traps with the caller. Errors within these function executions
cause the script that contains them to abort.
The special built-in command return is used to return from function
calls.
Function names can be listed with the -f or +f option of the typeset
special built-in command. The text of functions, when available, will
also be listed with -f. Functions can be undefined with the -f option
of the unset special built-in command.
Ordinarily, functions are unset when the shell executes a shell script.
Functions that need to be defined across separate invocations of the
shell should be placed in a directory and the FPATH variable should con-
tain the name of this directory. They may also be specified in the ENV
file.
Discipline Functions.
Each variable can have zero or more discipline functions associated with
it. The shell initially understands the discipline names get, set, ap-
pend, and unset but can be added when defining new types. On most sys-
tems others can be added at run time via the C programming interface ex-
tension provided by the builtin built-in utility. If the get discipline
is defined for a variable, it is invoked whenever the given variable is
referenced. If the variable .sh.value is assigned a value inside the
discipline function, the referenced variable will evaluate to this value
instead. If the set discipline is defined for a variable, it is invoked
whenever the given variable is assigned a value. If the append disci-
pline is defined for a variable, it is invoked whenever a value is ap-
pended to the given variable. The variable .sh.value is given the value
of the variable before invoking the discipline, and the variable will be
assigned the value of .sh.value after the discipline completes. If
.sh.value is unset inside the discipline, then that value is unchanged.
If the unset discipline is defined for a variable, it is invoked when-
ever the given variable is unset.
The variable .sh.name contains the name of the variable for which the
discipline function is called, .sh.subscript is the subscript of the
variable, and .sh.value will contain the value being assigned inside the
set discipline function. The variable _ is a reference to the variable
including the subscript if any. For the set discipline, changing
.sh.value will change the value that gets assigned. Finally, the expan-
sion ${var.name}, when name is the name of a discipline, and there is no
variable of this name, is equivalent to the command substitution ${
var.name;}.
Name Spaces.
Commands and functions that are executed as part of the list of a name-
space command that modify variables or create new ones, create a new
variable whose name is the name of the name space as given by identifier
preceded by .. When a variable whose name is name is referenced, it is
first searched for using .identifier.name. Similarly, a function de-
fined by a command in the namespace list is created using the name space
name preceded by a ..
When the list of a namespace command contains a namespace command, the
names of variables and functions that are created consist of the vari-
able or function name preceded by the list of identifiers each preceded
by ..
Outside of a name space, a variable or function created inside a name
space can be referenced by preceding it with the name space name.
By default, variables starting with .sh are in the sh name space.
Type Variables.
Typed variables provide a way to create data structure and objects. A
type can be defined either by a shared library, by the enum built-in
command described below, or by using the new -T option of the typeset
built-in command. With the -T option of typeset, the type name, speci-
fied as an option argument to -T, is set with a compound variable as-
signment that defines the type. Function definitions can appear inside
the compound variable assignment and these become discipline functions
for this type and can be invoked or redefined by each instance of the
type. The function name create is treated specially. It is invoked for
each instance of the type that is created but is not inherited and can-
not be redefined for each instance.
When a type is defined a special built-in command of that name is added.
These built-ins are declaration commands and follow the same expansion
rules as the built-in commands described below that are marked with a ‡
symbol. These commands can subsequently be used inside further type def-
initions. The man page for these commands can be generated by using the
--man option or any of the other -- options described with getopts. The
-r, -a, -A, -h, and -S options of typeset are permitted with each of
these new built-ins.
An instance of a type is created by invoking the type name followed by
one or more instance names. Each instance of the type is initialized
with a copy of the subvariables except for subvariables that are defined
with the -S option. Variables defined with the -S are shared by all in-
stances of the type. Each instance can change the value of any subvari-
able and can also define new discipline functions of the same names as
those defined by the type definition as well as any standard discipline
names. No additional subvariables can be defined for any instance.
When defining a type, if the value of a subvariable is not set and the
-r attribute is specified, it causes the subvariable to be a required
subvariable. Whenever an instance of a type is created, all required
subvariables must be specified. These subvariables become read-only in
each instance.
When unset is invoked on a subvariable within a type, and the -r at-
tribute has not been specified for this field, the value is reset to the
default value associative with the type. Invoking unset on a type in-
stance not contained within another type deletes all subvariables and
the variable itself.
A type definition can be derived from another type definition by defin-
ing the first subvariable name as _ and defining its type as the base
type. Any remaining definitions will be additions and modifications
that apply to the new type. If the new type name is the same as that of
the base type, the type will be replaced and the original type will no
longer be accessible.
The typeset command with the -T and no option argument or operands will
write all the type definitions to standard output in a form that can be
read in to create all they types.
Jobs.
If the monitor option of the set command is turned on, an interactive
shell associates a job with each pipeline. It keeps a table of current
jobs, printed by the jobs command, and assigns them small integer num-
bers. When a job is started asynchronously with &, the shell prints a
line which looks like:
[1] 1234
indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process ID was 1234.
If you are running a job and wish to do something else, you may hit the
key ^Z (control-Z) which sends a STOP signal to the current job. The
shell will then normally indicate that the job has been `Stopped', and
print another prompt. You can then manipulate the state of this job,
putting it in the background with the bg command, or run some other com-
mands and then eventually bring the job back into the foreground with
the foreground command fg. A ^Z takes effect immediately and is like an
interrupt in that pending output and unread input are discarded when it
is typed.
A job being run in the background will stop if it tries to read from the
terminal. Background jobs are normally allowed to produce output, but
this can be disabled by giving the command stty tostop. If you set this
tty option, then background jobs will stop when they try to produce out-
put like they do when they try to read input.
There are several ways to refer to jobs in the shell. A job can be re-
ferred to by the process ID of any process of the job or by one of the
following:
%number
The job with the given number.
%string
Any job whose command line begins with string.
%?string
Any job whose command line contains string.
%% Current job.
%+ Equivalent to %%.
%- Previous job.
The shell learns immediately whenever a process changes state. It nor-
mally informs you whenever a job becomes blocked so that no further
progress is possible, but only just before it prints a prompt. This is
done so that it does not otherwise disturb your work. The notify option
of the set command causes the shell to print these job change messages
as soon as they occur. If this happens while you are typing a command
with one of the built-in line editors active, the job change message ap-
pears above your input without disturbing your command entry.
When the monitor option is on, each background job that completes trig-
gers any trap set for CHLD.
When you try to leave the shell while jobs are running or stopped, you
will be warned that `You have stopped(running) jobs.' You may use the
jobs command to see what they are. If you immediately try to exit
again, the shell will not warn you a second time, and the stopped jobs
will be terminated. When a login shell receives a HUP signal, it sends
a HUP signal to each job that has not been disowned with the disown
built-in command described below.
Signals.
The INT and QUIT signals for an invoked command are ignored if the com-
mand is followed by & and the monitor option is not active. Otherwise,
signals have the values inherited by the shell from its parent (but see
also the trap built-in command below).
Execution.
Each time a command is read, the above expansions and substitutions are
carried out. If the command name matches one of the Special Built-in
Commands listed below, it is executed within the current shell process.
Next, the command name is checked to see if it matches a user defined
function. If it does, the positional parameters are saved and then re-
set to the arguments of the function call. A function is also executed
in the current shell process. When the function completes or issues a
return, the positional parameter list is restored. For functions de-
fined with the function name syntax, any trap set on EXIT within the
function is executed. The exit value of a function is the value of the
last command executed. If a command name is not a special built-in com-
mand or a user defined function, but it is one of the built-in commands
listed below, it is executed in the current shell process.
The shell variables PATH followed by the variable FPATH defines the list
of directories to search for the command name. Alternative directory
names are separated by a colon (:). The default path is the value that
was output by getconf PATH at the time ksh was compiled. The current
directory can be specified by two or more adjacent colons, or by a colon
at the beginning or end of the path list. If the command name contains
a /, then the search path is not used. Otherwise, each directory in the
list of directories defined by PATH and FPATH is checked in order. If
the directory being searched is contained in FPATH and contains a file
whose name matches the command being searched, then this file is loaded
into the current shell environment as if it were the argument to the .
command except that only preset aliases are expanded, and a function of
the given name is executed as described above.
If this directory is not in FPATH the shell first determines whether
there is a built-in version of a command corresponding to a given path-
name and if so it is invoked in the current process. If no built-in is
found, the shell checks for a file named .paths in this directory. If
found and there is a line of the form FPATH=path where path names an ex-
isting directory then that directory is searched immediately after the
current directory as if it were found in the FPATH variable. If path
does not begin with /, it is checked for relative to the directory being
searched.
The .paths file is then checked for a line of the form PLUGIN_LIB=lib-
name [ : libname ] ... . Each library named by libname will be searched
for as if it were an option argument to builtin -f, and if it contains a
built-in of the specified name this will be executed instead of a com-
mand by this name. Any built-in loaded from a library found this way
will be associated with the directory containing the .paths file so it
will only execute if not found in an earlier directory.
Finally, the directory will be checked for a file of the given name. If
the file has execute permission but is not an a.out file, it is assumed
to be a file containing shell commands. A separate shell is spawned to
read it. All non-exported variables are removed in this case. If the
.paths contains a line of the form name=value in the first or second
line, then the environment variable name is modified by prepending the
directory specified by value to the directory list. If value is not an
absolute directory, then it specifies a directory relative to the direc-
tory that the executable was found. If the environment variable name
does not already exist it will be added to the environment list for the
specified command. A parenthesized command is executed in a subshell
without removing non-exported variables.
Command Re-entry.
The text of the last HISTSIZE (default 512) commands entered from a ter-
minal device is saved in a history file. The file $HOME/.sh_history is
used if the HISTFILE variable is not set or if the file it names is not
writable. A shell can access the commands of all interactive shells
which use the same named HISTFILE. The built-in command hist is used to
list or edit a portion of this file. The portion of the file to be
edited or listed can be selected by number or by giving the first char-
acter or characters of the command. A single command or range of com-
mands can be specified. If you do not specify an editor program as an
argument to hist then the value of the variable HISTEDIT is used. If
HISTEDIT is unset, the obsolete variable FCEDIT is used. If FCEDIT is
not defined, then /bin/ed is used. The edited command(s) is printed and
re-executed upon leaving the editor unless you quit without writing.
The -s option (and in obsolete versions, the editor name -) is used to
skip the editing phase and to re-execute the command. In this case a
substitution parameter of the form old=new can be used to modify the
command before execution. For example, with the preset alias r, which
is aliased to ′hist -s′, typing `r bad=good c' will re-execute the most
recent command which starts with the letter c, replacing the first oc-
currence of the string bad with the string good.
History Expansion.
History expansions introduce words from the history list into the input
stream, making it easy to repeat commands, repeat arguments of a previ-
ous command in the current command, or fix typos in the previous com-
mand. The history expansion facility is an alternative to history con-
trol via the fc or hist built-in command. To enable it, turn on the -H
or histexpand option using the set command (see Built-in Commands be-
low).
History expansions begin with the character !. They may begin anywhere
in the input. The ! is passed unchanged with its special meaning dis-
abled when preceded by \ or ${, enclosed in single quotes, or followed
by a space, tab, newline, = or (. History expansions do not nest. They
are parsed separately before the shell parser is invoked, so they can
override shell grammar rules.
By default, the expanded version of any line that contains a history ex-
pansion is printed, added to the history, and then immediately executed.
History expansions are never added to the history themselves, regardless
of whether they succeed or fail due to an error. Normally, this means
that a command line with an erroneous history expansion is lost and
needs to be retyped from scratch, but if the histreedit shell option is
turned on and a line editor is active (see In-line Editing Options be-
low), the erroneous line is pre-filled into the next prompt's input
buffer for correcting. The histverify option causes the same to be done
for the results of successful history expansions, allowing verification
and editing before execution.
A history expansion may have an event specification, which indicates the
event from which words are to be taken, a word designator, which selects
particular words from the chosen event, and/or a modifier, which manipu-
lates the selected words.
An event specification can be:
n A number, referring to a particular event.
-n An offset, referring to the event n before the current
event.
# The current event.
! The previous event (equivalent to -1).
s The most recent event whose first word begins with the
string s.
?s? The most recent event which contains the string s. The sec-
ond ? can be omitted if it is immediately followed by a new-
line.
For example, consider this bit of someone's history list as might be
output by the hist -l command:
9 nroff -man wumpus.man
10 cp wumpus.man wumpus.man.old
11 vi wumpus.man
12 diff wumpus.man.old wumpus.man
The commands are shown with their event numbers. The current event,
which we haven't typed in yet, is event 13. !11 and !-2 refer to event
11. !! refers to the previous event, 12. !! can be abbreviated ! if it
is followed by : (see below). !n refers to event 9, which begins with
n. !?old? also refers to event 12, which contains old. Without word
designators or modifiers, history references simply expand to the entire
event, so we might type !cp to redo the copy command or !!|more if the
diff output scrolled off the top of the screen.
To select words from an event, the event specification can be followed
by a : and a designator for the desired words. The words of an input
line are numbered from 0, the first word (usually the command name) be-
ing 0, the second word (first argument) being 1, etc. The basic word
designators are:
0 The first word (command name).
n The nth argument.
^ The first argument, equivalent to 1.
$ The last argument.
% The word matched by the most recent ?s? search.
x-y A range of words.
-y Equivalent to 0-y.
* Equivalent to ^-$, but returns nothing if the event contains
only 1 word.
x* Equivalent to x-$.
x- Equivalent to x*, but omitting the last word ($).
Selected words are inserted into the command line separated by single
blanks. For example, the diff command in the previous example might
have been typed as diff !!:1.old !!:1 (using :1 to select the first ar-
gument from the previous event) or diff !-2:2 !-2:1 to select and swap
the arguments from the cp command. If we didn't care about the order of
the diff, we might have said diff !-2:1-2 or simply diff !-2:*. The cp
command might have been written cp wumpus.man !#:1.old, using # to refer
to the current event. !n:- hurkle.man would reuse the first two words
from the nroff command to say nroff -man hurkle.man.
The : separating the event specification from the word designator can be
omitted if the argument selector begins with a ^, $, *, % or -. For ex-
ample, our diff command might have been diff !!^.old !!^ or, equiva-
lently, diff !!$.old !!$. However, if !! is abbreviated !, an argument
selector beginning with - will be interpreted as an event specification.
The word(s) in a history reference can be edited by following them with
one or more modifiers, each preceded by a colon (:):
h Remove a trailing pathname component, leaving the head.
t Remove all leading pathname components, leaving the tail.
r Remove a filename extension .xxx, leaving the root name.
e Remove all but the extension.
s/l/r/ Substitute l for r. l is simply a string like r, not a reg-
ular expression as in the eponymous ed(1) command. Any
character may be used as the delimiter in place of /; a \
can be used to quote the delimiter inside l and r. The
character & in the r is replaced by l; \ also quotes &. If
l is empty, the l from the previous substitution is used, or
if there is none, the s from the most recent ?s? search.
The trailing delimiter may be omitted if it is immediately
followed by a newline.
& Repeat the previous substitution.
g Global substitution, for example :gs/foo/bar/ or :g&. Ap-
plies the s or & modifier to the entire command line.
a Same as g.
p Print the new command line but do not execute it.
q Quote the expanded words, preventing further expansions.
x Like q, but break into words at blanks, tabs and newlines.
Modifiers are applied to only the first modifiable word (unless g or a
is used). It is an error for no word to be modifiable.
For example, the diff command might have been written as diff wum-
pus.man.old !#^:r, using :r to remove .old from the first argument on
the same line (!#^). We might follow mail -s "I forgot my password" rot
with !:s/rot/root to correct the spelling of root.
History expansions also occur when an input line begins with ^. When it
is the first character on an input line, it is an abbreviation of !:s^.
Thus we might have said ^rot^root to make the spelling correction in the
previous example. This is the only history expansion that does not ex-
plicitly begin with !.
If a word on a command line begins with the history comment character #,
history expansion is ignored for the rest of that line. This usually
causes the shell parser (which uses the same character to signal a com-
ment) to treat the rest of the line as a comment as well, but as history
expansion is parsed separately from the shell grammar and with different
rules, this cannot be guaranteed in all cases. If the history comment
character is changed, the shell grammar comment character does not
change along with it.
The three characters used to signal history expansion can be changed us-
ing the histchars shell variable; see Shell Variables above.
In-line Editing Options.
Normally, each command line entered from a terminal device is simply
typed followed by a new-line (`RETURN' or `LINE FEED'). If either the
emacs, gmacs, or vi option is active, the user can edit the command
line. To be in either of these edit modes, set the corresponding op-
tion. An editing option is automatically selected each time the VISUAL
or EDITOR variable is assigned a value matching any of these editor
names; for details, see Shell Variables above under VISUAL.
The editing features require that the user's terminal accept `RETURN' as
carriage return without line feed and that a space (` ') must overwrite
the current character on the screen.
Unless the multiline option is on, the editing modes implement a concept
where the user is looking through a window at the current line. The
window width is the value of COLUMNS if it is defined, otherwise 80. If
the window width is too small to display the prompt and leave at least 8
columns to enter input, the prompt is truncated from the left. If the
line is longer than the window width minus two, a mark is displayed at
the end of the window to notify the user. As the cursor moves and
reaches the window boundaries, the window will be centered about the
cursor. The mark is a > (<, *) if the line extends on the right (left,
both) side(s) of the window.
The search commands in each edit mode provide access to the history
file. Only strings are matched, not patterns, although a leading ^ in
the string restricts the match to begin at the first character in the
line.
Each of the edit modes has an operation to list the files or commands
that match a partially entered word. When applied to the first word on
the line, or the first word after a ;, |, &, or (, and the word does not
begin with ∼ or contain a /, the list of aliases, functions, and exe-
cutable commands defined by the PATH variable that could match the par-
tial word is displayed. Otherwise, the list of files that match the
given word is displayed. If the partially entered word does not contain
any file expansion characters, a * is appended before generating these
lists. After displaying the generated list, the input line is redrawn.
These operations are called command name listing and file name listing,
respectively. There are additional operations, referred to as command
name completion and file name completion, which compute the list of
matching commands or files, but instead of printing the list, replace
the current word with a complete or partial match. For file name com-
pletion, if the match is unique, a / is appended if the file is a direc-
tory and a space is appended if the file is not a directory. Otherwise,
the longest common prefix for all the matching files replaces the word.
For command name completion, only the portion of the file names after
the last / are used to find the longest command prefix. If only a sin-
gle name matches this prefix, then the word is replaced with the command
name followed by a space. When using a tab for completion that does not
yield a unique match, a subsequent tab will provide a numbered list of
matching alternatives. A specific selection can be made by entering the
selection number followed by a tab. Neither completion nor listing op-
erations are attempted before the first character in a line.
Key Bindings.
The KEYBD trap can be used to intercept keys as they are typed and
change the characters that are actually seen by the shell. This trap is
executed after each character (or sequence of characters when the first
character is ESC) is entered while reading from a terminal. The vari-
able .sh.edchar contains the character or character sequence which gen-
erated the trap. Changing the value of .sh.edchar in the trap action
causes the shell to behave as if the new value were entered from the
keyboard rather than the original value.
The variable .sh.edcol is set to the input column number of the cursor
at the time of the input. The variable .sh.edmode is set to ESC when in
vi input mode (see below) and set to the empty string otherwise.
Prepending ${.sh.editmode} to a value assigned to .sh.edchar will cause
the shell to change to control mode if it is not already in this mode.
This trap is not invoked for characters entered as arguments to editing
directives, or while reading input for a character search.
Emacs Editing Mode.
This mode is entered by enabling either the emacs or gmacs option. The
only difference between these two modes is the way they handle ^T. To
edit, the user moves the cursor to the point needing correction and then
inserts or deletes characters or words as needed. All the editing com-
mands are control characters or escape sequences. The notation for con-
trol characters is caret (^) followed by the character. For example, ^F
is the notation for control F. This is entered by depressing `f' while
holding down the `CTRL' (control) key. The `SHIFT' key is not de-
pressed. (The notation ^? indicates the DEL (delete) key.)
The notation for escape sequences is M- followed by a character. For
example, M-f (pronounced Meta f) is entered by depressing ESC (ASCII
033) followed by `f'. (M-F would be the notation for ESC followed by
`SHIFT' (capital) `F'.)
All edit commands operate from any place on the line (not just at the
beginning). Neither the `RETURN' nor the `LINE FEED' key is entered af-
ter edit commands except when noted.
The M-[ multi-character commands below are DEC VT220 escape sequences
generated by special keys on standard PC keyboards, such as the arrow
keys. You could type them directly but they are meant to recognize the
keys in question, which are indicated in parentheses.
^F Move cursor forward (right) one character.
M-[C (Right arrow) Same as ^F.
M-f Move cursor forward one word. (The emacs editor's idea of a
word is a string of characters consisting of only letters,
digits and underscores.)
M-[1;3C (Alt-Right arrow) Same as M-f.
M-[1;5C (Ctrl-Right arrow) Same as M-f.
M-[1;9C (iTerm2 Alt-Right arrow) Same as M-f.
^B Move cursor backward (left) one character.
M-[D (Left arrow) Same as ^B.
M-b Move cursor backward one word.
M-[1;3D (Alt-Left arrow) Same as M-b.
M-[1;5D (Ctrl-Left arrow) Same as M-b.
M-[1;9D (iTerm2 Alt-Left arrow) Same as M-b.
^A Move cursor to start of line.
M-[H (Home) Same as ^A.
M-[1~ Same as ^A.
M-[7~ Same as ^A.
^E Move cursor to end of line.
M-[F (End) Same as ^E.
M-[4~ Same as ^E.
M-[8~ Same as ^E.
M-[Y Same as ^E.
M-OA (Up Arrow) Same as M-[A.
M-OB (Down Arrow) Same as M-[B.
M-OC (Right Arrow) Same as M-[C.
M-OD (Left Arrow) Same as M-[D.
M-O5C (Ctrl-Right Arrow) Same as M-f.
M-O5D (Ctrl-Left Arrow) Same as M-b.
^]char Move cursor forward to character char on current line.
M-^]char Move cursor backward to character char on current line.
^X^X Interchange the cursor and mark.
erase (User defined erase character as defined by the stty(1) com-
mand, usually ^H.) Delete previous character.
lnext (User defined literal next character as defined by the stty(1)
command, or ^V if not defined.) Removes the next character's
editing features (if any).
^D Delete current character.
M-[3~ (Forward delete) Same as ^D.
M-d Delete current word.
M-[3;5~ (Ctrl-Delete) Same as M-d.
M-^H (Meta-backspace) Delete previous word.
M-h Delete previous word.
M-^? (Meta-DEL) Delete previous word (if your interrupt character
is ^? (DEL, the default) then this command will not work).
^T Transpose current character with previous character and ad-
vance the cursor in emacs mode. Transpose two previous char-
acters in gmacs mode.
^C Capitalize current character.
M-c Capitalize current word.
M-l Change the current word to lower case.
^K Delete from the cursor to the end of the line. If preceded by
a numerical parameter whose value is less than the current
cursor position, then delete from given position up to the
cursor. If preceded by a numerical parameter whose value is
greater than the current cursor position, then delete from
cursor up to given cursor position.
^W Kill from the cursor to the mark.
M-p Push the region from the cursor to the mark on the stack.
kill (User defined kill character as defined by the stty(1) com-
mand, usually ^U.) Kill the entire current line. If two kill
characters are entered in succession, all kill characters from
then on cause a line feed (useful when using paper terminals).
A subsequent pair of kill characters undoes this change.
^Y Restore last item removed from line. (Yank item back to the
line.)
^X^E Return the command hist -e ${VISUAL:-${EDITOR:-vi}} in the in-
put buffer to call a full editor — vi by default — on the cur-
rent command line.
^L Line feed and print current line.
M-^L Clear the screen.
^@ (Null character) Set mark.
M-space (Meta space) Set mark.
^J (New line) Execute the current line.
^M (Return) Execute the current line.
eof End-of-file character, normally ^D, is processed as an End-of-
file only if the current line is empty.
^P Fetch previous command. Each time ^P is entered the previous
command back in time is accessed. Moves back one line when
not on the first line of a multi-line command.
M-[A (Up arrow) If the cursor is at the end of the line, it is
equivalent to ^R with string set to the contents of the cur-
rent line. Otherwise, it is equivalent to ^P.
M-< Fetch the least recent (oldest) history line.
M-> Fetch the most recent (youngest) history line.
^N Fetch next command line. Each time ^N is entered the next
command line forward in time is accessed.
M-[B (Down arrow) Equivalent to ^N.
^Rstring Reverse search history for a previous command line containing
string. If a parameter of zero is given, the search is for-
ward. String is terminated by a `RETURN' or `NEW LINE'. If
string is preceded by a ^, the matched line must begin with
string. If string is omitted, then the next command line con-
taining the most recent string is accessed. In this case a
parameter of zero reverses the direction of the search.
^G Exit reverse search mode.
^O Operate - Execute the current line and fetch the next line
relative to current line from the history file.
M-digits (Escape) Define numeric parameter, the digits are taken as a
parameter to the next command. The commands that accept a pa-
rameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-.,
M-^], M-_, M-=, M-b, M-c, M-d, M-f, M-h, M-l, M-^H, and the
arrow keys and forward-delete key.
M-letter Soft-key - Your alias list is searched for an alias by the
name _letter and if an alias of this name is defined, its
value will be inserted on the input queue. The letter must
not be one of the above meta-functions.
M-[letter Soft-key - Your alias list is searched for an alias by the
name __letter and if an alias of this name is defined, its
value will be inserted on the input queue. This can be used
to program function keys on many terminals.
M-. The last word of the previous command is inserted on the line.
If preceded by a numeric parameter, the value of this parame-
ter determines which word to insert rather than the last word.
M-_ Same as M-..
M-* Attempt pathname expansion on the current word. An asterisk
is appended if the word doesn't match any file or contain any
special pattern characters.
M-ESC Command or file name completion as described above.
^I tab Attempts command or file name completion as described above.
If a partial completion occurs, repeating this will behave as
if M-= were entered. If no match is found or entered after
space, a tab is inserted.
M-= If not preceded by a numeric parameter, it generates the list
of matching commands or file names as described above. Other-
wise, the word under the cursor is replaced by the item corre-
sponding to the value of the numeric parameter from the most
recently generated command or file list. If the cursor is not
on a word, it is inserted instead.
^U Multiply parameter of next command by 4.
\ If the backslashctrl shell option is on (which is the default
setting), this escapes the next character. Editing charac-
ters, the user's erase, kill and interrupt (normally ^C) char-
acters may be entered in a command line or in a search string
if preceded by a \. The \ removes the next character's edit-
ing features (if any). See also lnext which is not subject to
any shell option.
M-^V Display version of the shell.
M-[2~ (Insert) Escape the next character.
M-# If the line does not begin with a #, a # is inserted at the
beginning of the line and after each new-line, and the line is
entered. This causes a comment to be inserted in the history
file. If the line begins with a #, the # is deleted and one #
after each new-line is also deleted.
Vi Editing Mode.
There are two typing modes. Initially, when you enter a command you are
in the input mode. To edit, the user enters control mode by typing ESC
(033) and moves the cursor to the point needing correction and then in-
serts or deletes characters or words as needed. Most control commands
accept an optional repeat count prior to the command.
The notation for control characters used below is ^ followed by a char-
acter. For instance, ^H is entered by holding down the Control key and
pressing H. ^[ (Control+[) is equivalent to the ESC key. The notation
for escape sequences is ^[ followed by one or more characters.
The ^[[ (ESC [) multi-character commands below are DEC VT220 escape se-
quences generated by special keys on standard PC keyboards, such as the
arrow keys, which are indicated in parentheses. When in input mode,
these keys will switch you to control mode before performing the associ-
ated action. These sequences can use preceding repeat count parameters,
but only when the ^[ and the subsequent [ are entered into the input
buffer at the same time, such as when pressing one of those keys.
Input Edit Commands
By default the editor is in input mode.
erase (User defined erase character as defined by the stty(1)
command, usually ^H or #.) Delete previous character.
^W Delete the previous blank separated word.
eof As the first character of the line causes the shell to
terminate unless the ignoreeof option is set. Other-
wise this character is ignored.
lnext (User defined literal next character as defined by the
stty(1) or ^V if not defined.) Removes the next char-
acter's editing features (if any).
\ If the backslashctrl shell option is on (which is the
default setting), this escapes the next erase or kill
character.
^I tab Attempts command or file name completion as described
above and returns to input mode. If a partial comple-
tion occurs, repeating this will behave as if = were
entered from control mode. If no match is found or en-
tered after space, a tab is inserted.
Motion Edit Commands
These commands will move the cursor.
[count]l Cursor forward (right) one character.
[count]^[[C
(Right arrow) Same as l.
[count]w Cursor forward one alphanumeric word.
[count]W Cursor to the beginning of the next word that follows a
blank.
[count]e Cursor to end of word.
[count]E Cursor to end of the current blank delimited word.
[count]h Cursor backward (left) one character.
[count]^[[D
(Left arrow) Same as h.
[count]b Cursor backward one word.
[count]B Cursor to preceding blank separated word.
[count]| Cursor to column count.
[count]fc Find the next character c in the current line.
[count]Fc Find the previous character c in the current line.
[count]tc Equivalent to f followed by h.
[count]Tc Equivalent to F followed by l.
[count]; Repeats count times, the last single character find
command, f, F, t, or T.
[count], Reverses the last single character find command count
times.
0 Cursor to start of line.
^[[H (Home) Same as 0.
^[[1~ Same as 0.
^[[7~ Same as 0.
^[[1;3D (Alt-Left arrow) Same as b.
^[[1;5D (Ctrl-Left arrow) Same as b.
^[[1;9D (iTerm2 Alt-Left arrow) Same as b.
^[[1;3C (Alt-Right arrow) Same as w.
^[[1;5C (Ctrl-Right arrow) Same as w.
^[[1;9C (iTerm2 Alt-Right arrow) Same as w.
^[[2~ (Insert) Same as i.
^[[3;5~ (Ctrl-Delete) Same as dw.
^[OA (Up Arrow) Same as ^[[A.
^[OB (Down Arrow) Same as ^[[B.
^[OC (Right Arrow) Same as ^[[C.
^[OD (Left Arrow) Same as ^[[D.
^[O5C (Ctrl-Right Arrow) Same as w.
^[O5D (Ctrl-Left Arrow) Same as b.
^ Cursor to first non-blank character in line.
$ Cursor to end of line.
^[[F (End) Same as $.
^[[4~ Same as $.
^[[8~ Same as $.
^[[Y Same as $.
^G Exit reverse search mode.
% Moves to balancing (, ), {, }, [, or ]. If cursor is
not on one of the above characters, the remainder of
the line is searched for the first occurrence of one of
the above characters first.
Search Edit Commands
These commands access your command history.
[count]k Fetch previous command. Each time k is entered the
previous command back in time is accessed.
[count]- Equivalent to k.
[count]^[[A
(Up arrow) If cursor is at the end of the line it is
equivalent to / with string set to the contents of the
current line. Otherwise, it is equivalent to k.
[count]j Fetch next command. Each time j is entered the next
command forward in time is accessed.
[count]+ Equivalent to j.
[count]^[[B
(Down arrow) Equivalent to j.
[count]G The command number count is fetched. The default is
the least recent history command.
/string Search backward through history for a previous command
containing string. String is terminated by a `RETURN'
or `NEW LINE'. If string is preceded by a ^, the
matched line must begin with string. If string is
empty, the previous string will be used.
?string Same as / except that search will be in the forward di-
rection.
n Search for next match of the last pattern to / or ?
commands.
N Search for next match of the last pattern to / or ?,
but in reverse direction.
Text Modification Edit Commands
These commands will modify the line.
a Enter input mode and enter text after the current char-
acter.
A Append text to the end of the line. Equivalent to $a.
[count]cmotion
c[count]motion
Delete current character through the character that mo-
tion would move the cursor to and enter input mode. If
motion is c, the entire line will be deleted and input
mode entered.
C Delete the current character through the end of line
and enter input mode. Equivalent to c$.
S Equivalent to cc.
[count]s Replace characters under the cursor in input mode.
D Delete the current character through the end of line.
Equivalent to d$.
[count]dmotion
d[count]motion
Delete current character through the character that mo-
tion would move to. If motion is d , the entire line
will be deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the first non-blank character.
Equivalent to ^i.
[count]P Place the previous text modification before the cursor.
[count]p Place the previous text modification after the cursor.
R Enter input mode and replace characters on the screen
with characters you type overlay fashion.
[count]rc Replace the count character(s) starting at the current
cursor position with c, and advance the cursor.
[count]x Delete current character.
[count]^[[3~
(Forward delete) Same as x.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
[count]∼ Invert the case of the count character(s) starting at
the current cursor position and advance the cursor.
[count]_ Causes the count word of the previous command to be ap-
pended and input mode entered. The last word is used
if count is omitted.
* Causes an * to be appended to the current word and
pathname expansion attempted. If no match is found, it
rings the bell. Otherwise, the word is replaced by the
matching pattern and input mode is entered.
\ Command or file name completion as described above.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion
Yank current character through character that motion
would move the cursor to and puts them into the delete
buffer. The text and cursor are unchanged.
yy Yanks the entire line.
Y Yanks from current position to end of line. Equivalent
to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands performed on the
line.
[count]v Returns the command hist -e ${VISUAL:-${EDITOR:-vi}}
count in the input buffer to call a full editor — vi by
default — on a history entry. If count is omitted,
then the current line is used.
^L Line feed and print current line. Has effect only in
control mode.
^J (New line) Execute the current line, regardless of
mode.
^M (Return) Execute the current line, regardless of mode.
# If the first character of the command is a #, then this
command deletes this # and each # that follows a new-
line. Otherwise, sends the line after inserting a # in
front of each line in the command. Useful for causing
the current line to be inserted in the history as a
comment and uncommenting previously commented commands
in the history file.
[count]= If count is not specified, it generates the list of
matching commands or file names as described above.
Otherwise, the word under the cursor is replaced by the
count item from the most recently generated command or
file list. If the cursor is not on a word, it is in-
serted instead.
@letter Your alias list is searched for an alias by the name
_letter and if an alias of this name is defined, its
value will be inserted on the input queue for process-
ing.
^V Display version of the shell.
Built-in Commands.
The simple-commands listed below are built in to the shell and are exe-
cuted in the same process as the shell. The effects of any added In-
put/Output redirections are local to the command, except for the exec
and redirect commands. Unless otherwise indicated, the output is writ-
ten on standard output (file descriptor 1) and the exit status, when
there is no syntax error, is zero. Except for :, true, false, and echo,
all built-in commands accept -- to indicate end of options, and are
self-documenting.
The self-documenting commands interpret the option --man as a request to
display that command's own manual page, --help as a request to display
the OPTIONS section from their manual page, and -? as a request to
print a brief usage message. All these are processed as error messages,
so they are written on standard error (file descriptor 2) and to pipe
them into a pager such as more(1) you need to add a 2>&1 redirection be-
fore the |. The display of boldface text depends on whether standard er-
ror is on a terminal, so is disabled when using a pager. Exporting the
ERROR_OPTIONS environment variable with a value containing emphasis will
force this on; a value containing noemphasis forces it off. The test/[
command needs an additional -- argument to recognize self-documentation
options, e.g. test --man --. The exec and redirect commands, as they
make redirections permanent, should use self-documentation options in a
subshell when redirecting, for example: (redirect --man) 2>&1. There
are advanced output options as well; see getopts --man for more informa-
tion.
Commands that are preceded by a † symbol below are special built-in com-
mands and are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in
effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. They are not valid function names.
Commands that are preceded by a ‡ symbol below are declaration commands.
Any following words that are in the format of a variable assignment are
expanded with the same rules as a variable assignment. This means that
tilde expansion is performed after the = sign, array assignments of the
form varname=(assign_list) are supported, and field splitting and path-
name expansion are not performed.
† : [ arg ... ]
The command only expands parameters.
† . name [ arg ... ]
If name is a function defined with the function name reserved
word syntax, the function is executed in the current environment
(as if it had been defined with the name() syntax). Otherwise if
name refers to a file, the file is read in its entirety and the
commands are executed in the current shell environment. The
search path specified by PATH is used to find the directory con-
taining the file. If any arguments arg are given, they become
the positional parameters while processing the . command and the
original positional parameters are restored upon completion.
Otherwise the positional parameters are unchanged. The exit sta-
tus is the exit status of the last command executed.
[ expression ]
The [ command is the same as test, with the exception that an ad-
ditional closing ] argument is required. See test below.
alias [ -ptx ] [ name[ =value ] ] ...
alias with no arguments prints the list of aliases in the form
name=value on standard output. The -p option causes the word
alias to be inserted before each one. When one or more arguments
are given, an alias is defined for each name whose value is
given. A trailing space in value causes the next word to be
checked for alias substitution. With the -t option, alias acts
like hash; see there. Without the -t option, for each name in
the argument list for which no value is given, the name and value
of the alias is printed. The obsolete -x option has no effect in
most contexts, although if it's used with -t it will suppress all
output. The exit status is non-zero if a name is given, but no
value, and no alias has been defined for the name.
autoload name ...
Marks each name undefined so that the FPATH variable will be
searched to find the function definition when the function is
referenced. The same as typeset -fu.
bg [ job... ]
This command is only on systems that support job control. Puts
each specified job into the background. The current job is put
in the background if job is not specified. See Jobs for a de-
scription of the format of job.
† break [ n ]
Exit from the enclosing for, while, until, or select loop, if
any. If n is specified, then break n levels.
builtin [ -ds ] [ -f file ] [ name ... ]
If name is not specified, and no -f option is specified, the
built-ins are printed on standard output. The -s option prints
only the special built-ins. Otherwise, each name represents the
pathname whose basename is the name of the built-in. The entry
point function name is determined by prepending b_ to the built-
in name. A built-in specified by a pathname will only be exe-
cuted when that pathname would be found during the path search.
Built-ins found in libraries loaded via the .paths file will as-
sociate with the pathname of the directory containing the .paths
file.
The ISO C/C++ prototype is b_mycommand(int argc, char *argv[],
void *context) for the builtin command mycommand where argv is
array an of argc elements and context is an optional pointer to a
Shell_t structure as described in <ast/shell.h>.
Special built-ins cannot be bound to a pathname or deleted. The
-d option deletes each of the given built-ins. On systems that
support dynamic loading, the -f option names a shared library
containing the code for built-ins. The shared library prefix
and/or suffix, which depend on the system, can be omitted. Once
a library is loaded, its symbols become available for subsequent
invocations of builtin. Multiple libraries can be specified with
separate invocations of the builtin command. Libraries are
searched in the reverse order in which they are specified. When
a library is loaded, it looks for a function in the library whose
name is lib_init() and invokes this function with an argument of
0.
cd [ -L ] [ -eP ] [ arg ]
cd [ -L ] [ -eP ] old new
This command can be in either of two forms. In the first form it
changes the current directory to arg. If arg is - the directory
is changed to the previous directory. The shell variable HOME is
the default arg. The variable PWD is set to the current direc-
tory. The shell variable CDPATH defines the search path for the
directory containing arg. Alternative directory names are sepa-
rated by a colon (:). The default path is the empty string
(specifying the current directory). Note that the current direc-
tory may be specified by a dot (.) or by an empty path name, ei-
ther of which can appear immediately after the equal sign or be-
tween the colon delimiters anywhere else in the path list. If
arg begins with a / then the search path is not used. Otherwise,
each directory in the path is searched for arg.
The second form of cd substitutes the string new for the string
old in the current directory name, PWD, and tries to change to
this new directory.
By default, symbolic link names are treated literally when find-
ing the directory name. This is equivalent to the -L option.
The -P option causes symbolic links to be resolved when determin-
ing the directory. The last instance of -L or -P on the command
line determines which method is used.
If -e and -P are both in effect and the correct PWD could not be
determined after successfully changing the directory, cd will re-
turn with exit status one and produce no output. If any other
error occurs while both flags are active, the exit status is
greater than one.
The cd command may not be executed by rksh.
command [ -pvxV ] name [ arg ... ]
With the -v option, command is equivalent to the built-in whence
command described below. The -V option causes command to act
like whence -v.
Without the -v or -V options, command executes name with the ar-
guments given by arg. Functions and aliases will not be searched
for when finding name. If name refers to a special built-in, as
marked with † in this manual, command disables the special prop-
erties described above for that mark, executing the command as a
regular built-in. (For example, using command set -o option-name
prevents a script from terminating when an invalid option name is
given.)
The -p option causes the operating system's standard utilities
path (as output by getconf PATH) to be searched rather than the
one defined by the value of PATH.
The -x option searches for name as an external command, bypassing
built-ins. If the arguments contain at least one word that ex-
pands to multiple arguments, for example *.txt or "$@", then the
-x option also allows executing external commands with argument
lists that are longer than the operating system allows. This
functionality is similar to xargs(1) but is easier to use. The
shell does this by invoking the external command multiple times
if needed, dividing the expanded argument list over the invoca-
tions. Any arguments that come before the first word that expands
to multiple arguments, as well as any that follow the last such
word, are repeated for each invocation. This allows each invoca-
tion to use the same command options, as well as the same trail-
ing destination arguments for commands like cp(1) or mv(1). When
all invocations are completed, command -x exits with the status
of the invocation that had the highest exit status. (Note that
command -x may still fail with an "argument list too long" error
if a single argument exceeds the maximum length of the argument
list, or if a long arguments list contains no word that expands
to multiple arguments.)
‡ compound vname[=value] ...
Causes each vname to be a compound variable. The same as type-
set -C.
† continue [ n ]
Resume the next iteration of the enclosing for, while, until, or
select loop. If n is specified, then resume at the n-th enclos-
ing loop.
disown [ job... ]
Causes the shell not to send a HUP signal to each given job, or
all active jobs if job is omitted, when a login shell terminates.
echo [ arg ... ]
When the first arg does not begin with a -, and none of the argu-
ments contain a \, then echo prints each of its arguments sepa-
rated by a space and terminated by a new-line. Otherwise, the
behavior of echo is system dependent and print or printf de-
scribed below should be used. See echo(1) for usage and descrip-
tion.
‡ enum [ -i ] type[=(value ...) ] ...
Creates, for each type specified, an enumeration type declaration
command named type. Variables of the created type can only store
any one of the values given. For example, enum bool=(false true)
creates a Boolean variable type of which variables may be de-
clared like bool x=true y=false. If =(value ...) is omitted,
then type must be an indexed array variable with at least two el-
ements and the values are taken from this array variable. If -i
is specified the values are case-insensitive. Declaration com-
mands are created as special builtins that cannot be removed or
overridden by shell functions. Each created declaration command
has a --man option that shows documentation on its type's behav-
ior and possible values.
Within arithmetic expressions (see Arithmetic Evaluation above),
enumeration type values translate to index numbers between 0 and
the number of defined values minus 1. It is an error for an
arithmetic expression to assign a value outside of that range.
Decimal fractions are ignored. Taking the bool type from the ex-
ample above, if a variable of this type is used in an arithmetic
expression, false translates to 0 and true to 1. Enumeration
values may also be used directly in an arithmetic expression that
refers to a variable of an enumeration type. To continue our ex-
ample, for a bool variable v, ((v==true)) is the same as ((v==1))
and if a variable named true exists, it is ignored.
† eval [ arg ... ]
The arguments are read as input to the shell and the resulting
command(s) executed.
† exec [ -c ] [ -a name ] [ arg ... ]
If arg is given, the command specified by the arguments is
seaerched on PATH as an external command and executed in place of
the current shell without creating a new process. The value of
the SHLVL environment variable is decreased by one, unless the
shell replaced is a subshell. The -c option causes the environ-
ment to be cleared before applying variable assignments associ-
ated with the exec invocation. The -a option causes name rather
than the first arg, to become argv[0] for the new process. If
arg is not given and only I/O redirections are given, then this
command persistently modifies file descriptors as in redirect.
† exit [ n ]
Causes the shell to exit with the exit status specified by n.
The value will be the least significant 8 bits of n (if speci-
fied) or of the exit status of the last command executed. An
end-of-file will also cause the shell to exit, except for an in-
teractive shell that has the ignoreeof option turned on (see set
below).
†‡ export [ -p ] [ name[=value] ] ...
If name is not given, the names and values of each variable with
the export attribute are printed with the values quoted in a man-
ner that allows them to be re-input. The export command is the
same as typeset -x except that if you use export within a func-
tion, no local variable is created. The -p option causes the
word export to be inserted before each one. Otherwise, the given
names are marked for automatic export to the environment of sub-
sequently-executed commands.
false Does nothing, and exits 1. Used with until for infinite loops.
fc [ -e ename ] [ -N num ] [ -nlr ] [ first [ last ] ]
fc -s [ old=new ] [ command ]
The same as hist.
fg [ job... ]
This command is only on systems that support job control. Each
job specified is brought to the foreground and waited for in the
specified order. Otherwise, the current job is brought into the
foreground. See Jobs for a description of the format of job.
‡ float vname[=value] ...
Declares each vname to be a long floating point number. The same
as typeset -lE.
functions [ -Stux ] [ name ... ]
Lists functions. The same as typeset -f.
getconf [ name [ pathname ] ]
Prints the current value of the configuration parameter given by
name. The configuration parameters are defined by the IEEE POSIX
1003.1 and IEEE POSIX 1003.2 standards. (See pathconf(2) and
sysconf(3).) The pathname argument is required for parameters
whose value depends on the location in the file system. If no
arguments are given, getconf prints the names and values of the
current configuration parameters. The pathname / is used for
each of the parameters that requires pathname.
getopts [ -a name ] optstring vname [ arg ... ]
Checks arg for legal options. If arg is omitted, the positional
parameters are used. An option argument begins with a + or a -.
An option not beginning with + or - or the argument -- ends the
options. Options beginning with + are only recognized when opt-
string begins with a +. optstring contains the letters that
getopts recognizes. If a letter is followed by a :, that option
is expected to have an argument. The options can be separated
from the argument by blanks. The option -? causes getopts to
generate a usage message on standard error. The -a argument can
be used to specify the name to use for the usage message, which
defaults to $0.
getopts places the next option letter it finds inside variable
vname each time it is invoked. The option letter will be
prepended with a + when arg begins with a +. The index of the
next arg is stored in OPTIND. The option argument, if any, gets
stored in OPTARG.
A leading : in optstring causes getopts to store the letter of an
invalid option in OPTARG, and to set vname to ? for an unknown
option and to : when a required option argument is missing. Oth-
erwise, getopts prints an error message. The exit status is non-
zero when there are no more options.
There is no way to specify any of the options :, +, -, ?, [, and
]. The option # can only be specified as the first option.
hash [ -r ] [ utility ... ]
hash displays or modifies the hash table with the locations of
recently used programs. If given no arguments, it lists all com-
mand/path associations (a.k.a. 'tracked aliases') in the hash ta-
ble. Otherwise, hash performs a PATH search for each utility sup-
plied and adds the result to the hash table. Any utility that is
not found is silently ignored. The -r option empties the hash
table. This can also be achieved by resetting PATH.
hist [ -e ename ] [ -N num ] [ -nlr ] [ first [ last ] ]
hist -s [ old=new ] [ command ]
In the first form, a range of commands from first to last is se-
lected from the last HISTSIZE commands that were typed at the
terminal. The arguments first and last may be specified as a
number or as a string. A string is used to locate the most re-
cent command starting with the given string. A negative number
is used as an offset to the current command number. If the -l
option is selected, the commands are listed on standard output.
Otherwise, the editor program ename is invoked on a file contain-
ing these keyboard commands. If ename is not supplied, then the
value of the variable HISTEDIT is used. If HISTEDIT is not set,
then FCEDIT (default /bin/ed) is used as the editor. When edit-
ing is complete, the edited command(s) is executed if the changes
have been saved. If last is not specified, then it will be set
to first. If first is not specified, the default is the previous
command for editing and -16 for listing. The option -r reverses
the order of the commands and the option -n suppresses command
numbers when listing. In the second form, command is interpreted
as first described above and defaults to the last command exe-
cuted. The resulting command is executed after the optional sub-
stitution old=new is performed. The option -N causes hist to
start num commands back.
‡ integer vname[=value] ...
Declares each vname to be a long integer number. The same as
typeset -li.
jobs [ -lnp ] [ job ... ]
Lists information about each given job; or all active jobs if job
is omitted. The -l option lists process IDs in addition to the
normal information. The -n option only displays jobs that have
stopped or exited since last notified. The -p option causes only
the process group to be listed. See Jobs for a description of
the format of job.
kill [ -s signame ] job ...
kill [ -n signum ] job ...
kill -Ll [ sig ... ]
Sends either the TERM (terminate) signal or the specified signal
to the specified jobs or processes. Signals are either given by
number with the -n option or by name with the -s option (as given
in <signal.h>, stripped of the prefix ``SIG''. For backward com-
patibility, the n and s can be omitted and the number or name
placed immediately after the -. If the signal being sent is TERM
(terminate) or HUP (hangup), and the posix shell option is off,
then the job or process will be sent a CONT (continue) signal if
it is stopped. The argument job can be the process ID of a
process that is not a member of one of the active jobs. See Jobs
for a description of the format of job. In the third form, kill
-l or kill -L, if sig is not specified, the signal names are
listed. The -l option lists only the signal names. The -L op-
tion lists each signal name and corresponding number. Otherwise,
for each sig that is a name, the corresponding signal number is
listed. For each sig that is a number, the signal name corre-
sponding to the least significant 8 bits of sig is listed.
let arg ...
Each arg is a separate arithmetic expression to be evaluated.
let only recognizes octal numbers starting with 0 when the set
option letoctal is on. See Arithmetic Evaluation above for a de-
scription of arithmetic expression evaluation.
The exit status is 0 if the value of the last expression is non-
zero, and 1 otherwise.
‡ nameref vname[=refname] ...
Declares each vname to be a variable name reference. The same as
typeset -n.
print [ -CRenprsv ] [ -u unit ] [ -f format ] [ arg ... ]
With no options or with option - or --, each arg is printed on
standard output. The -f option causes the arguments to be
printed as described by printf. In this case, any e, n, r, R op-
tions are ignored. Otherwise, unless the -C, -R, -r, or -v are
specified, the following escape conventions will be applied:
\a The alert character (ASCII 07).
\b The backspace character (ASCII 010).
\c Causes print to end without processing more arguments and
not adding a new-line.
\f The formfeed character (ASCII 014).
\n The newline character (ASCII 012).
\r The carriage return character (ASCII 015).
\t The tab character (ASCII 011).
\v The vertical tab character (ASCII 013).
\E The escape character (ASCII 033).
\\ The backslash character \.
\0x The character defined by the 1, 2, or 3-digit octal string
given by x.
The -R option will print all subsequent arguments and options
other than -n. The -e causes the above escape conventions to be
applied. This is the default behavior. It reverses the effect
of an earlier -r. The -p option causes the arguments to be writ-
ten onto the pipe of the process spawned with |& instead of stan-
dard output. The -v option treats each arg as a variable name
and writes the value in the printf %B format. The -C option
treats each arg as a variable name and writes the value in the
printf %#B format. The -s option causes the arguments to be
written onto the history file instead of standard output. The -u
option can be used to specify a one digit file descriptor unit
number unit on which the output will be placed. The default is
1. If the option -n is used, no new-line is added to the output.
printf [ -v vname ] format [ arg ... ]
The arguments arg are printed on standard output in accordance
with the ANSI C formatting rules associated with the format
string format. If the number of arguments exceeds the number of
format specifications, the format string is reused to format re-
maining arguments. The following extensions can also be used:
%b A %b format can be used instead of %s to cause escape se-
quences in the corresponding arg to be expanded as de-
scribed in print.
%B A %B option causes each of the arguments to be treated as
variable names and the binary value of variable will be
printed. The alternate flag # causes a compound variable
to be output on a single line. This is most useful for
compound variables and variables whose attribute is -b.
%H A %H format can be used instead of %s to cause characters
in arg that are special in HTML and XML to be output as
their entity name. The alternate flag # formats the out-
put for use as a URI.
%p A %p format will convert the given number to hexadecimal.
%P A %P format can be used instead of %s to cause arg to be
interpreted as an extended regular expression and be
printed as a shell pattern.
%q A %q format can be used instead of %s to cause the result-
ing string to be quoted in a manner than can be reinput to
the shell. When q is preceded by the alternative format
specifier, #, the string is quoted in manner suitable as a
field in a .csv format file.
%(date-format)T
A %(date-format)T format can be used to treat an argument
as a date/time string and to format the date/time accord-
ing to the date-format.
%Q A %Q format will convert the given number of seconds to
readable time.
%R A %R format can be used instead of %s to cause arg to be
interpreted as a shell pattern and to be printed as an ex-
tended regular expression.
%Z A %Z format will output a byte whose value is 0.
%d The precision field of the %d format can be followed by a
. and the output base. In this case, the # flag charac-
ter causes base# to be prepended. When an output base is
specified without giving a precision (e.g. %..2d), the
precision defaults to 1 instead of 0.
# The # flag, when used with the %d format without an output
base, displays the output in powers of 1000 indicated by
one of the following suffixes: k M G T P E, and when used
with the %i format displays the output in powers of 1024
indicated by one of the following suffixes: Ki Mi Gi Ti Pi
Ei.
= The = flag centers the output within the specified field
width.
L The L flag, when used with the %c or %s formats, treats
precision as character width instead of byte count.
, The , flag, when used with the %d or %f formats, separates
groups of digits with the grouping delimiter (, on groups
of 3 in the C locale).
The -v option assigns the output directly to a variable instead
of writing it to standard output. This is faster than capturing
the output using a command substitution and avoids the latter's
stripping of final linefeed characters (\n). The vname argument
should be a valid variable name, optionally with one or more ar-
ray subscripts in square brackets. Note that square brackets
should be quoted to avoid pathname expansion.
On some systems, the external printf(1) command allows the format
operand to begin with a - without any preceding -- option termi-
nator argument for compatibility with ancient scripts, provided
no options are given. On such systems, ksh's built-in printf may
have been built to be as compatible with this as possible while
still allowing its options to be usable. However, the POSIX
standard requires adding the preceding -- to keep such a format
operand from being misinterpreted as options. The obsolete syn-
tax is not portable and should be avoided in new scripts.
pwd [ -LP ]
Outputs the value of the current working directory. The -L op-
tion is the default; it prints the logical name of the current
directory. If the -P option is given, all symbolic links are re-
solved from the name. The last instance of -L or -P on the com-
mand line determines which method is used.
read [ -ACSaprsv ] [ -d delim ] [ -n n ] [ -N n ] [ -t timeout ] [ -u
unit ] [ vname?prompt ] [ vname ... ]
The shell input mechanism. One line is read and is broken up
into fields using the characters in IFS as separators. The es-
cape character, \, is used to remove any special meaning for the
next character and for line continuation. The first field is as-
signed to the first vname, the second field to the second vname,
etc., with leftover fields assigned to the last vname. If vname
is omitted, then REPLY is used as the default vname. When vname
has the binary attribute and -n or -N is specified, the bytes
that are read are stored directly into the variable. If you ap-
pend ?prompt to the first vname, then read will display prompt on
standard error before reading if standard input is a terminal or
pipe; the ? should be quoted to protect it from pathname expan-
sion. The exit status is 0 unless an end-of-file is encountered
or read has timed out. The options for the read command have
meaning as follows:
-A Causes the variable vname to be unset and each field that
is read to be stored in successive elements of the in-
dexed array vname.
-C Causes the variable vname to be read as a compound vari-
able. Blanks will be ignored when finding the beginning
open parenthesis.
-N Causes n bytes to be read unless an end-of-file has been
encountered or the read times out because of the -t op-
tion.
-S Causes the line to be treated like a record in a .csv
format file so that double quotes can be used to allow
the delimiter character and the new-line character to ap-
pear within a field.
-a Same as -A.
-d Causes the read to continue to the first character of de-
lim instead of the newline control character. Multibyte
characters for delim are not supported.
-n Causes at most n bytes to be read instead of a full line,
but will return when reading from a slow device as soon
as any characters have been read.
-p Input is read from the current co-process spawned by the
shell using ⎪&. An end-of-file causes read to disconnect
the co-process so that another can be created.
-r Raw mode. The \ character is not treated specially.
-s The input will be saved as a command in the history file.
-t Used to specify a timeout in seconds when reading from a
terminal or pipe.
-u This option can be used to specify a one-digit file de-
scriptor unit unit to read from. The file descriptor can
be opened with the exec or redirect built-in command. If
unit is p, input is read from the current co-process as
with the -p option. The default value of unit is 0.
-v The value of the first vname will be used as a default
value when reading from a terminal device.
†‡ readonly [ -p ] [ vname[=value] ] ...
If vname is not given, the names and values of each variable with
the read-only attribute is printed with the values quoted in a
manner that allows them to be re-input. The -p option causes the
word readonly to be inserted before each one. Otherwise, the
given vnames are marked read-only and these names cannot be
changed by subsequent assignment. Unlike typeset -r , readonly
does not create a function-local scope and the given vnames are
marked globally read-only by default. When defining a type, if
the value of a read-only subvariable is not defined, the value is
required when creating each instance.
redirect
This command only accepts input/output redirections. It can open
and close files and modify file descriptors from 0 to 9 as speci-
fied by the input/output redirection list (see the Input/Output
section above), with the difference that the effect persists past
the execution of the redirect command. When invoking another
program, file descriptors greater than 2 that were opened with
this mechanism are only passed on if they are explicitly redi-
rected to themselves as part of the invocation (e.g. 4>&4) or if
the posix option is set.
† return [ n ]
Causes a shell function, dot script (see . and source), or pro-
file script to return to the invoking shell environment with the
exit status specified by n. This status value can use the full
signed integer range as shown by the commands getconf INT_MIN and
getconf INT_MAX. A value outside that range will produce a warn-
ing and an exit status of 128. If n is omitted, then the value
of $? is assumed, i.e., the exit status of the last command exe-
cuted is passed on. If return is invoked while not in a func-
tion, dot script, or profile script, then it behaves the same as
exit.
† set [ ±BCGHabefhkmnprstuvx ] [ ±o [ option ] ] ... [ ±A vname ] [ arg
... ]
The options for this command have meaning as follows:
-A Array assignment. Unset the variable vname and assign
values sequentially from the arg list. If +A is used,
the variable vname is not unset first.
-B Enable brace group expansion. On by default, except if
ksh is invoked as sh or rsh.
-C Prevents redirection > from truncating existing files.
Files that are created are opened with the O_EXCL mode.
Requires >| to truncate a file when turned on.
-G Enables recursive pathname expansion. This adds the dou-
ble-star pattern ** to the pathname expansion (see Path-
name Expansion above). By itself, it matches the recur-
sive contents of the current directory, which is to say,
all files and directories in the current directory and in
all its subdirectories, sub-subdirectories, and so on.
If the pathname pattern ends in **/, only directories and
subdirectories are matched, including symbolic links that
point to directories. A prefixed directory name is not
included in the results unless that directory was itself
found by a pattern. For example, dir/** matches the re-
cursive contents of dir but not dir itself, whereas
di[r]/** matches both dir itself and the recursive con-
tents of dir. Symbolic links to non-directories are not
followed. Symbolic links to directories are followed if
they are specified literally or match a pattern as de-
scribed under Pathname Expansion, but not if they result
from a double-star pattern.
-H Enable !-style history expansion similar to csh(1). See
History Expansion above.
-a All variables that are assigned a value while this option
is on are automatically exported, unless they have a dot
in their name. Variables created in namespaces declared
with the namespace keyword (see Name Spaces above) are
only exported while their name space is active.
-b Prints job completion messages as soon as a background
job changes state rather than waiting for the next
prompt. If one of the shell line editors is in use (see
In-line Editing Options above), the completion message is
inserted directly above the command line being typed.
-e Unless contained in a || or && command, or the command
following an if while or until command or in the pipeline
following !, if a command has a non-zero exit status, ex-
ecute the ERR trap, if set, and exit. This mode is dis-
abled while reading profiles.
-f Disables pathname expansion.
-h Obsolete; no effect.
-k All variable assignment arguments are placed in the envi-
ronment for a command, not just those that precede the
command name.
-m Background jobs will run in a separate process group and
a line will print upon completion. The exit status of
background jobs is reported in a completion message. A
pipeline will not terminate until all component commands
of the pipeline have terminated. On systems with job
control, this option is turned on automatically for in-
teractive shells.
-n Read commands and check them for syntax errors, but do
not execute them. Ignored for interactive shells.
-o The following argument can be one of the following option
names:
allexport
Same as -a.
backslashctrl
The backslash character \ escapes the next con-
trol character in the emacs built-in editor and
the next erase or kill character in the vi built-
in editor. On by default.
bgnice All background jobs are run at a lower priority.
This is the default mode.
braceexpand
Same as -B.
emacs Activates the emacs-style command line editor.
See Emacs Editing Mode above.
errexit Same as -e.
functrace
Causes the -x option's state and the DEBUG trap
action to be inherited by functions defined using
the function keyword (see Functions above) in-
stead of being reset to default. Changes made to
them within the function do not propagate back to
the parent scope. Similarly, this option also
causes the DEBUG trap action to be inherited by
subshells.
globcasedetect
When this option is turned on, globbing (see
Pathname Expansion above) and file name listing
and completion (see In-line Editing Options
above) automatically become case-insensitive on
file systems where the difference between upper-
and lowercase is ignored for file names. This is
transparently determined for each directory, so a
path pattern that spans multiple file systems can
be part case-sensitive and part case-insensitive.
In more precise terms, each slash-separated path
name component pattern p is treated as ~(i:p) if
its parent directory exists on a case-insensitive
file system. This option is only present on op-
erating systems that support case-insensitive
file systems.
globstar
Same as -G.
gmacs Activates the emacs-style command line editor
with modified ^T. See Emacs Editing Mode above.
histexpand
Same as -H.
histreedit
If a history expansion (see -H) fails, the com-
mand line is reloaded into the next prompt's edit
buffer, allowing corrections.
histverify
The results of a history expansion (see -H) are
not immediately executed. Instead, the expanded
line is loaded into the next prompt's edit
buffer, allowing further changes.
ignoreeof
An interactive shell will not exit on end-of-
file. The command exit must be used.
keyword Same as -k.
letoctal
The let command allows octal numbers starting
with 0. On by default if ksh is invoked as sh or
rsh.
markdirs
All directory names resulting from pathname ex-
pansion have a trailing / appended.
monitor Same as -m.
multiline
The built-in editors will use multiple lines on
the screen for lines that are longer than the
width of the screen. This may not work for all
terminals. The shell uses the system default
tput(1) command to obtain the terminal escape
codes for the necessary operations. Multi-line
editing is disabled if this fails. On most sys-
tems, setting the TERM variable to your termi-
nal's type and exporting it corrects this situa-
tion. The multiline option is ineffectual on
systems whose tput(1) command supports neither
terminfo(5) nor termcap(5) capability names.
noclobber
Same as -C.
noexec Same as -n.
noglob Same as -f.
nolog Obsolete; has no effect.
notify Same as -b.
nounset Same as -u.
pipefail
The exit status of the entire pipeline will be
that of the last component command that exited
with a non-zero exit status, or zero if no com-
mand exited with a non-zero exit status. The
shell will wait for all component commands of the
pipeline to terminate, instead of only waiting
for the last component command.
posix Enables the POSIX standard mode for maximum com-
patibility with other compliant shells. At the
moment that the posix option is turned on, it
also turns on letoctal and turns off -B/braceex-
pand; the reverse is done when posix is turned
back off. (These options can still be controlled
independently in between.) Furthermore, the posix
option is automatically turned on upon invocation
if the shell is invoked as sh or rsh, or if -o
posix or --posix is specified on the shell invo-
cation command line, or when executing scripts
without a #! path with this option active in the
invoking shell. In that case, the invoked shell
will not import type attributes for variables
(such as integer or left/right justify) from the
environment.
In addition, while on, the posix option
• disables exporting variable type attributes to
the environment for other ksh processes to im-
port;
• disallows brace expansion on the results of
unquoted expansions (if the -B/braceexpand op-
tion is turned back on);
• disables the special handling of repeated is-
space class characters in the IFS variable;
• causes redirect and exec to open file descrip-
tors > 2 without the close-on-exec flag, so
that they are left open when invoking another
program;
• disables the &> redirection shorthand;
• disables fast filescan loops of type while in-
putredirection ;do list ;done;
• makes the <> redirection operator default to
redirecting standard input if no file descrip-
tor number precedes it;
• causes the shell to use a standard UNIX
pipe(2) instead of a socketpair(2) to connect
commands in a pipeline (when reading directly
from a pipeline, the <#pattern and <##pattern
redirection operators will not work and the -n
option to the read built-in will not return
early when reading from a slow device);
• disables the special floating point constants
Inf and NaN in arithmetic evaluation so that,
e.g., $((inf)) and $((nan)) refer to the vari-
ables by those names;
• enables the recognition of a leading zero as
introducing an octal number in all arithmetic
evaluation contexts, except in the let built-
in while letoctal is off;
• disables zero-padding of seconds in the output
of the time and times built-ins;
• stops the . command (but not source) from
looking up functions defined with the function
syntax;
• disables the recognition of unexpanded shell
arithmetic expressions for the numerical con-
version specifiers of the printf built-in com-
mand, causing them to print a warning for
operands that are not valid decimal, 0x-pre-
fixed hexadecimal or 0-prefixed octal numbers;
• stops the kill built-in command from automati-
cally sending a CONT signal to stopped jobs or
processes upon sending a HUP or TERM signal;
• disables the special handling of /dev/fd/n in
file existence and access test operators in
test/[ and [[, causing these to operate on the
file /dev/fd/n in the file system;
• disables the recognition of unexpanded shell
arithmetic expressions in the numerical com-
parison operators -eq, -ne, -gt, -ge, -lt and
-le of the test/[ built-in command, causing
them to accept only decimal numbers as
operands;
• changes the test/[ built-in command to make
its deprecated expr1 -a expr2 and expr1 -o
expr2 operators work even if expr1 equals "!"
or "(" (which means the nonstandard unary -a
file and -o option operators cannot be di-
rectly negated using ! or wrapped in parenthe-
ses); and
• disables a hack that makes test -t ([ -t ])
equivalent to test -t 1 ([ -t 1 ]).
privileged
Same as -p.
showme When enabled, simple commands or pipelines pre-
ceded by a semicolon (;) will be displayed as if
the xtrace option were enabled but will not be
executed. Otherwise, the leading ; will be ig-
nored.
trackall
Same as -h.
verbose Same as -v.
vi Activates the vi-style command line editor, ini-
tially in input mode. See Vi Editing Mode above.
viraw Obsolete; has no effect.
xtrace Same as -x.
If no option name is supplied, then the current option
settings are printed.
-p Disables processing of the $HOME/.profile file and uses
the file /etc/suid_profile instead of the ENV file. This
mode is on whenever the effective UID (GID) is not equal
to the real UID (GID). Turning this off causes the ef-
fective UID and GID to be set to the real UID and GID.
-r Enables the restricted shell. This option cannot be un-
set once set.
-s Sort the positional parameters lexicographically.
-t (Obsolete). Exit after reading and executing one com-
mand.
-u Treat unset parameters as an error when substituting. $@
and $* are exempt.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are executed.
-- Do not change any of the options; useful in setting $1 to
a value beginning with -. If no arguments follow this
option then the positional parameters are unset.
As an obsolete feature, if the first arg is - then the -x and -v
options are turned off and the next arg is treated as the first
argument. Using + rather than - causes these options to be
turned off. These options can also be used upon invocation of
the shell. The current set of options may be found in $-. Un-
less -A is specified, the remaining arguments are positional pa-
rameters and are assigned, in order, to $1 $2 .... If no argu-
ments are given, then the names and values of all variables are
printed on the standard output.
† shift [ n ]
The positional parameters from $n+1 ... are renamed $1 ... , de-
fault n is 1. The parameter n can be any arithmetic expression
that evaluates to a non-negative number less than or equal to $#.
sleep [ -s ] duration
Suspends execution for the number of decimal seconds or fractions
of a second given by duration. duration can be an integer,
floating point value or ISO 8601 duration specifying the length
of time to sleep. The option -s causes the sleep builtin to ter-
minate when it receives any signal. If duration is not specified
in conjunction with -s, sleep will wait for a signal indefi-
nitely.
source name [ arg ... ]
Same as ., except it is not treated as a special built-in com-
mand.
stop job ...
Sends a SIGSTOP signal to one or more processes specified by job,
suspending them until they receive SIGCONT. The same as
kill -s STOP.
suspend
Sends a SIGSTOP signal to the main shell process, suspending the
script or child shell session until it receives SIGCONT (for in-
stance, when typing fg in the parent shell). Equivalent to
kill -s STOP "$$", except that it accepts no operands and refuses
to suspend a login shell.
test expression
The test and [ commands execute conditional expressions similar
to those specified for the [[ compound command under Conditional
Expressions above, but with several important differences. The =,
== and != operators test for string (in)equality without pattern
matching; == is nonstandard and unportable. The && and || opera-
tors are not available. Instead, the -a and -o binary operators
can be used, but they are fraught with pitfalls due to grammati-
cal ambiguities and therefore deprecated in favor of invoking
separate test commands. Most importantly, as test and [ are sim-
ple regular commands, field splitting and pathname expansion are
performed on all their arguments and all aspects of regular shell
grammar (such as redirection) remain active. This is usually
harmful, so care must be taken to quote arguments and expansions
to avoid this. To avoid the many pitfalls arising from these is-
sues, the [[ compound command should be used instead. The primary
purpose of the test and [ commands is compatibility with other
shells that lack [[.
The test/[ command does not parse options except if there are two
arguments and the second is --. To access the inline documenta-
tion with an option such as --man, you need one of the forms
test --man -- or [ --man -- ].
times Displays the accumulated user and system CPU times, one line with
the times used by the shell and another with those used by all of
the shell's child processes. No options are supported. Seconds
are zero-padded unless the posix shell option is on.
† trap [ -p ] [ action ] [ sig ] ...
The -p option causes the trap action associated with each trap as
specified by the arguments to be printed with appropriate quot-
ing. Otherwise, action will be processed as if it were an argu-
ment to eval when the shell receives signal(s) sig. Each sig can
be given as a number or as the name of the signal. Trap commands
are executed in order of signal number. Any attempt to set a
trap on a signal that was ignored on entry to the current shell
is ineffective. If action is omitted and the first sig is a num-
ber, or if action is -, then the trap(s) for each sig are reset
to their original values. If action is the empty string, then
this signal is ignored by the shell and by the commands it in-
vokes. If sig is ERR then action will be executed whenever a
command has a non-zero exit status. If sig is DEBUG then action
will be executed before each command. The variable .sh.command
will contain the current command line when action is running, in
the same format as the output generated by the xtrace option (mi-
nus the preceding PS4 prompt). If the exit status of the trap is
2 the command will not be executed. If the exit status of the
trap is 255 and inside a function or a dot script, the function
or dot script will return. If sig is 0 or EXIT and the trap
statement is executed inside the body of a function defined with
the function name syntax, then the command action is executed af-
ter the function completes. If sig is 0 or EXIT for a trap set
outside any function then the command action is executed on exit
from the shell. If sig is KEYBD, then action will be executed
whenever a key is read while in emacs, gmacs, or vi mode. The
trap command with no arguments prints a list of commands associ-
ated with each signal number.
An exit or return without an argument in a trap action will preserve the
exit status of the command that invoked the trap.
true Does nothing, and exits 0. Used with while for infinite loops.
type [ -afpPqt ] name ...
The same as whence -v.
†‡ typeset [ ±ACHSbflmnprstux ] [ ±EFLRXZi[n] ] [ +-M [ mapname ] ] [
-T [ tname=(assign_list) ] ] [ -h str ] [ -a [ [type] ] ] [
vname[=value ] ] ...
Sets attributes and values for shell variables and functions.
When invoked inside a function defined with the function name
syntax, a new instance of the variable vname is created, and the
variable's value and type are restored when the function com-
pletes. The following list of attributes may be specified:
-A Declares vname to be an associative array. Subscripts are
strings rather than arithmetic expressions.
-C Causes each vname to be a compound variable. If value
names a compound variable, it is copied into vname. Oth-
erwise, the empty compound value is assigned to vname.
-a Declares vname to be an indexed array. This is the de-
fault. Subscripts are numerical and start at 0. To make
it possible to use alphanumeric enumeration constants of a
given type as subscripts, an option value of the form
[type] can be specified (including the surrounding square
brackets), which should be quoted to avoid pathname expan-
sion), where type must be the name of an enumeration type
created with the enum command.
-E Declares vname to be a double precision floating point
number. If n is non-zero, it defines the number of sig-
nificant figures that are used when expanding vname. Oth-
erwise, ten significant figures will be used.
-F Declares vname to be a double precision floating point
number. If n is non-zero, it defines the number of places
after the decimal point that are used when expanding
vname. Otherwise ten places after the decimal point will
be used.
-H This option provides UNIX to host-name file mapping on
non-UNIX machines.
-L Left justify and remove leading blanks from value. If n
is non-zero, it defines the width of the field, otherwise
it is determined by the width of the value of first as-
signment. When the variable is assigned to, it is filled
on the right with blanks or truncated, if necessary, to
fit into the field. The -R option is turned off.
-M Use the character mapping mapping defined by wctrans(3).
such as tolower and toupper when assigning a value to each
of the specified operands. When mapping is specified and
there are not operands, all variables that use this map-
ping are written to standard output. When mapping is
omitted and there are no operands, all mapped variables
are written to standard output.
-R Right justify and fill with leading blanks. If n is non-
zero, it defines the width of the field, otherwise it is
determined by the width of the value of first assignment.
The field is left filled with blanks or truncated from the
end if the variable is reassigned. The -L option is
turned off.
-S When used within the assign_list of a type definition, it
causes the specified subvariable to be shared by all in-
stances of the type. When used inside a function defined
with the function reserved word, the specified variables
will have function static scope. Otherwise, the variable
is unset prior to processing the assignment list.
-T If followed by tname, it creates a type named by tname us-
ing the compound assignment assign_list to tname. Other-
wise, it writes all the type definitions to standard out-
put.
-X Declares vname to be a double precision floating point
number and expands using the %a format of ISO-C99. If n
is non-zero, it defines the number of hex digits after the
radix point that is used when expanding vname. The de-
fault is 10.
-Z Right justify and fill with leading zeros if the first
non-blank character is a digit and the -L option has not
been set. Remove leading zeros if the -L option is also
set. If n is non-zero, it defines the width of the field,
otherwise it is determined by the width of the value of
first assignment.
-f The names refer to function names rather than variable
names. No assignments can be made and the only other
valid options are -S, -t, -u and -x. The -S can be used
with discipline functions defined in a type to indicate
that the function is static. For a static function, the
same method will be used by all instances of that type no
matter which instance references it. In addition, it can
only use value of variables from the original type defini-
tion. These discipline functions cannot be redefined in
any type instance. The -t option turns on execution trac-
ing for this function. The -u option causes this function
to be marked undefined. The FPATH variable will be
searched to find the function definition when the function
is referenced. If no options other than -f is specified,
then the function definition will be displayed on standard
output. If +f is specified, then a line containing the
function name followed by a shell comment containing the
line number and path name of the file where this function
was defined, if any, is displayed. The exit status can be
used to determine whether the function is defined so that
typeset -f .sh.math.name will return 0 when math function
name is defined and non-zero otherwise.
-b The variable can hold any number of bytes of data. The
data can be text or binary. The value is represented by
the base64 encoding of the data. If -Z is also specified,
the size in bytes of the data in the buffer will be deter-
mined by the size associated with the -Z. If the base64
string assigned results in more data, it will be trun-
cated. Otherwise, it will be filled with bytes whose
value is zero. The printf format %B can be used to output
the actual data in this buffer instead of the base64 en-
coding of the data.
-g Forces variables to be created or modified at the global
scope, even when typeset is executed in a function defined
by the function name syntax (see Functions above) or in a
name space (see Name Spaces above).
-h Used within type definitions to add information when gen-
erating information about the subvariable on the man page.
It is ignored when used outside of a type definition.
When used with -f the information is associated with the
corresponding discipline function.
-i Declares vname to be represented internally as integer.
The right hand side of an assignment is evaluated as an
arithmetic expression when assigning to an integer. If n
is non-zero, it defines the output arithmetic base, other-
wise the output base will be ten.
-l Used with -i, -E or -F, to indicate long integer, or long
float. Otherwise, all uppercase characters are converted
to lowercase. The uppercase option, -u, is turned off.
Equivalent to -M tolower .
-m Moves or renames the variable. The value is the name of a
variable whose value will be moved to vname. The original
variable will be unset. Cannot be used with any other op-
tions.
-n Declares vname to be a reference to the variable whose
name is defined by the value of variable vname. This is
usually used to reference a variable inside a function
whose name has been passed as an argument. Cannot be used
with other options except -g.
-p The name, attributes and values for the given vnames are
written on standard output in a form that can be used as
shell input. If +p is specified, then the values are not
displayed.
-r The given vnames are marked read-only and these names can-
not be changed by subsequent assignment.
-s When given along with -i, restricts integer size to short.
-t Tags the variables. Tags are user definable and have no
special meaning to the shell.
-u When given along with -i, specifies unsigned integer.
Otherwise, all lowercase characters are converted to up-
percase. The lowercase option, -l, is turned off. Equiv-
alent to -M toupper .
-x The given vnames are marked for automatic export to the
environment of subsequently-executed commands. Variables
whose names contain a . cannot be exported.
The -i, -F, -E, and -X options cannot be specified along with -R,
-L, or -Z. The -b option cannot be specified along with -L, -u,
or -l. The -f, -m, -n, and -T options cannot be used together
with any other option.
Using + rather than - causes these options to be turned off. If
no vname arguments are given, a list of vnames (and optionally
the values) of the variables is printed. (Using + rather than -
keeps the values from being printed.) The -p option causes type-
set followed by the option letters to be printed before each name
rather than the names of the options. If any option other than
-p is given, only those variables which have all of the given op-
tions are printed. Otherwise, the vnames and attributes of all
variables that have attributes are printed.
ulimit [ -HSaMctdfkxlqenVuPpmrRbiswTv ] [ limit ]
Set or display a resource limit. The available resource limits
are listed below. Many systems do not support one or more of
these limits. The limit for a specified resource is set when
limit is specified. The value of limit can be a number in the
unit specified below with each resource, or the value unlimited.
The -H and -S options specify whether the hard limit or the soft
limit for the given resource is set. A hard limit cannot be in-
creased once it is set. A soft limit can be increased up to the
value of the hard limit. If neither the H nor S option is speci-
fied, the limit applies to both. The current resource limit is
printed when limit is omitted. In this case, the soft limit is
printed unless H is specified. When more than one resource is
specified, then the limit name and unit is printed before the
value.
-a Lists all of the current resource limits.
-b The socket buffer size in bytes.
-c The number of 512-byte blocks on the size of core dumps.
-d The number of K-bytes on the size of the data area.
-e The scheduling priority.
-f The number of 512-byte blocks on files that can be written
by the current process or by child processes (files of any
size may be read).
-i The signal queue size.
-k The max number of kqueues created by the current user.
-l The locked address space in K-bytes.
-M The address space limit in K-bytes.
-m The number of K-bytes on the size of physical memory.
-n The number of file descriptors plus 1.
-P The max number of pseudo-terminals created by the current
user.
-p The number of 512-byte blocks for pipe buffering.
-q The message queue size in K-bytes.
-R The max time a real-time process can run before blocking,
in microseconds. If this limit is exceeded the process is
sent a SIGXCPU signal.
-r The max real-time priority.
-s The number of K-bytes on the size of the stack area.
-T The number of threads.
-t The number of CPU seconds to be used by each process.
-u The number of processes.
-V The number of open vnode monitors.
-v The number of K-bytes for virtual memory.
-w The swap size in K-bytes.
-x The number of file locks.
If no option is given, -f is assumed.
umask [ -S ] [ mask ]
The user file-creation mask is set to mask (see umask(2)). mask
can either be an octal number or a symbolic value as described in
chmod(1). If a symbolic value is given, the new umask value is
the complement of the result of applying mask to the complement
of the previous umask value. If mask is omitted, the current
value of the mask is printed. The -S option causes the mode to
be printed as a symbolic value. Otherwise, the mask is printed
in octal.
unalias [ -a ] name ...
The aliases given by the list of names are removed from the alias
list. The -a option causes all the aliases to be unset.
† unset [ -fnv ] vname ...
The variables given by the list of vnames are unassigned, i.e.,
except for subvariables within a type, their values and attrib-
utes are erased. For subvariables of a type, the values are re-
set to the default value from the type definition. Readonly
variables cannot be unset. If the -f option is set, then the
names refer to function names. If the -v option is set, then the
names refer to variable names. The -f option overrides -v. If
-n is set and name is a name reference, then name will be unset
rather than the variable that it references. The default is
equivalent to -v. Unsetting LINENO, MAILCHECK, OPTARG, OPTIND,
RANDOM, SECONDS, TMOUT, and _ removes their special meaning even
if they are subsequently assigned to.
wait [ job ... ]
Wait for the specified job and report its termination status. If
job is not given, then all currently active child processes are
waited for. The exit status from this command is that of the
last process waited for if job is specified; otherwise it is
zero. See Jobs for a description of the format of job.
whence [ -afpPqtv ] name ...
For each name, indicate how it would be interpreted if used as a
command name.
The -v option produces a more verbose report. The -f option
skips the search for functions. The -p and -P options do a path
search for name even if name is an alias, a function, or a re-
served word. Both of these options turn off the -v option. The
-q option causes whence to enter quiet mode. whence will return
zero if all arguments are built-ins, functions, or are programs
found on the path. The -t option only outputs the type of the
given command. Like -p and -P, -t will turn off the -v option.
The -a option is similar to the -v option but causes all inter-
pretations of the given name to be reported.
Invocation.
If the shell is invoked by exec(2), initialization depends on argument
zero ($0) as follows. If the first character of $0 is -, or the -l op-
tion is given on the invocation command line, then the shell is assumed
to be a login shell. If the basename of the command path in $0 is rsh,
rksh, or krsh, then the shell becomes restricted. If the basename is sh
or rsh, or the -o posix option is given on the invocation command line,
then the shell is initialized in full POSIX compliance mode (see the set
builtin command above for more information). After this, if the shell
was assumed to be a login shell, commands are read from /etc/profile and
then from $HOME/.profile if it exists. Alternatively, the option -l
causes the shell to be treated as a login shell. Next, for interactive
shells, commands are read from the file named by ENV if the file exists,
its name being determined by performing parameter expansion, command
substitution, and arithmetic expansion on the value of that environment
variable. If the -s option is not present and arg and a file by the
name of arg exists, then it reads and executes this script. Otherwise,
if the first arg does not contain a /, a path search is performed on the
first arg to determine the name of the script to execute. The script
arg must have execute permission and any setuid and setgid settings will
be ignored. If the script is not found on the path, arg is processed as
if it named a built-in command or function. Commands are then read as
described below; the following options are interpreted by the shell when
it is invoked:
-D A list of all double quoted strings that are preceded by a $
will be printed on standard output and the shell will exit.
This set of strings will be subject to language translation when
the locale is not C or POSIX. No commands will be executed.
-E or -o rc or --rc
Read the file named by the ENV variable or by $HOME/.kshrc if
not defined after the profiles. On by default for interactive
shells. Use +E, +o rc or --norc to turn off.
-c Read and execute a script from the first arg instead of a file.
The second arg, if present, becomes that script's command name
($0). Any third and further args become positional parameters
starting at $1.
-s Read and execute a script from standard input instead of a file.
The command name ($0) cannot be set. Any args become the posi-
tional parameters starting at $1. This option is forced on if
no arg is given and is ignored if -c is also specified.
-i or -o interactive or --interactive
If the -i option is present or if the shell's standard input and
standard error are attached to a terminal (as told by tcge-
tattr(3)), then this shell is interactive. In this case TERM is
ignored (so that kill 0 does not kill an interactive shell) and
INTR is caught and ignored (so that wait is interruptible). In
all cases, QUIT is ignored by the shell.
-r or -o restricted or --restricted
If the -r option is present, the shell is a restricted shell.
The remaining options and arguments are described under the set command
above. An optional - as the first argument is ignored.
Rksh Only.
Rksh is used to set up login names and execution environments whose ca-
pabilities are more controlled than those of the standard shell. The
actions of rksh are identical to those of ksh, except that the following
are disallowed:
• unsetting the restricted option
• changing directory (see cd(1))
• setting or unsetting the value or attributes of SHELL,
ENV, FPATH, or PATH
• specifying path or command names containing /
• redirecting output (>, >|, <>, and >>)
• adding or deleting built-in commands
• using command -p to invoke a command
The restrictions above are enforced after .profile and the ENV files are
interpreted.
When a command to be executed is found to be a shell procedure, rksh in-
vokes ksh to execute it. Thus, it is possible to provide to the end-
user shell procedures that have access to the full power of the standard
shell, while imposing a limited menu of commands; this scheme assumes
that the end-user does not have write and execute permissions in the
same directory.
The net effect of these rules is that the writer of the .profile has
complete control over user actions, by performing guaranteed setup ac-
tions and leaving the user in an appropriate directory (probably not the
login directory).
The system administrator often sets up a directory of commands (e.g.,
/usr/rbin) that can be safely invoked by rksh.
EXIT STATUS
Errors detected by the shell, such as syntax errors, cause the shell to
return a non-zero exit status. If the shell is being used non-interac-
tively, then execution of the shell file is abandoned unless the error
occurs inside a subshell in which case the subshell is abandoned. Oth-
erwise, the shell returns the exit status of the last command executed
(see also the exit command above). Run time errors detected by the
shell are reported by printing the command or function name and the er-
ror condition. If the line number that the error occurred on is greater
than one, then the line number is also printed in square brackets ([])
after the command or function name.
FILES
/etc/profile
The system wide initialization file, executed for login shells.
$HOME/.profile
The personal initialization file, executed for login shells after
/etc/profile.
$HOME/.kshrc
Default personal initialization file, executed for interactive
shells when ENV is not set.
/etc/suid_profile
Alternative initialization file, executed instead of the personal
initialization file when the real and effective user or group ID
do not match.
/dev/null
The null device.
SEE ALSO
cat(1), cd(1), chmod(1), cut(1), date(1), echo(1), emacs(1), env(1),
gmacs(1), grep(1), stty(1), test(1), umask(1), vi(1), dup(2), exec(2),
fork(2), getpwnam(3), ioctl(2), lseek(2), paste(1), pathconf(2),
pipe(2), sysconf(3), umask(2), ulimit(2), wait(2), strftime(3), wc-
trans(3), rand(3), profile(5), environ(7).
Morris I. Bolsky and David G. Korn, The New KornShell Command and Pro-
gramming Language, Prentice Hall, 1995.
POSIX - Part 2: Shell and Utilities, IEEE Std 1003.2-1992, ISO/IEC
9945-2, IEEE, 1993.
CAVEATS
If a command is executed, and then a command with the same name is in-
stalled in a directory in the search path before the directory where the
original command was found, the shell will continue to exec the original
command. Use the hash command or the -t option of the alias command to
correct this situation.
Using the hist built-in command within a compound command will cause the
whole command to disappear from the history file.
The built-in command . file reads the whole file before any commands are
executed. Therefore, alias and unalias commands in the file will not
apply to any commands defined in the file.
Traps are not processed while a job is waiting for a foreground process.
Thus, a trap on CHLD won't be executed until the foreground job termi-
nates.
In locales that use a multibyte character set such as UTF-8, the KEYBD
trap is only triggered for ASCII characters (1-127).
It is a good idea to leave a space after the comma operator in arith-
metic expressions to prevent the comma from being interpreted as the
decimal point character in certain locales.
KSH(1)
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