IPC::Run(3pm) User Contributed Perl Documentation IPC::Run(3pm)
NAME
IPC::Run - system() and background procs w/ piping, redirs, ptys (Unix,
Win32)
SYNOPSIS
## First,a command to run:
my @cat = qw( cat );
## Using run() instead of system():
use IPC::Run qw( run timeout );
run \@cat, \$in, \$out, \$err, timeout( 10 ) or die "cat: $?";
# Can do I/O to sub refs and filenames, too:
run \@cat, '<', "in.txt", \&out, \&err or die "cat: $?";
run \@cat, '<', "in.txt", '>>', "out.txt", '2>>', "err.txt";
# Redirecting using pseudo-terminals instead of pipes.
run \@cat, '<pty<', \$in, '>pty>', \$out_and_err;
## Scripting subprocesses (like Expect):
use IPC::Run qw( start pump finish timeout );
# Incrementally read from / write to scalars.
# $in is drained as it is fed to cat's stdin,
# $out accumulates cat's stdout
# $err accumulates cat's stderr
# $h is for "harness".
my $h = start \@cat, \$in, \$out, \$err, timeout( 10 );
$in .= "some input\n";
pump $h until $out =~ /input\n/g;
$in .= "some more input\n";
pump $h until $out =~ /\G.*more input\n/;
$in .= "some final input\n";
finish $h or die "cat returned $?";
warn $err if $err;
print $out; ## All of cat's output
# Piping between children
run \@cat, '|', \@gzip;
# Multiple children simultaneously (run() blocks until all
# children exit, use start() for background execution):
run \@foo1, '&', \@foo2;
# Calling \&set_up_child in the child before it executes the
# command (only works on systems with true fork() & exec())
# exceptions thrown in set_up_child() will be propagated back
# to the parent and thrown from run().
run \@cat, \$in, \$out,
init => \&set_up_child;
# Read from / write to file handles you open and close
open IN, '<in.txt' or die $!;
open OUT, '>out.txt' or die $!;
print OUT "preamble\n";
run \@cat, \*IN, \*OUT or die "cat returned $?";
print OUT "postamble\n";
close IN;
close OUT;
# Create pipes for you to read / write (like IPC::Open2 & 3).
$h = start
\@cat,
'<pipe', \*IN, # may also be a lexical filehandle e.g. \my $infh
'>pipe', \*OUT,
'2>pipe', \*ERR
or die "cat returned $?";
print IN "some input\n";
close IN;
print <OUT>, <ERR>;
finish $h;
# Mixing input and output modes
run \@cat, 'in.txt', \&catch_some_out, \*ERR_LOG;
# Other redirection constructs
run \@cat, '>&', \$out_and_err;
run \@cat, '2>&1';
run \@cat, '0<&3';
run \@cat, '<&-';
run \@cat, '3<', \$in3;
run \@cat, '4>', \$out4;
# etc.
# Passing options:
run \@cat, 'in.txt', debug => 1;
# Call this system's shell, returns TRUE on 0 exit code
# THIS IS THE OPPOSITE SENSE OF system()'s RETURN VALUE
run "cat a b c" or die "cat returned $?";
# Launch a sub process directly, no shell. Can't do redirection
# with this form, it's here to behave like system() with an
# inverted result.
$r = run "cat a b c";
# Read from a file in to a scalar
run io( "filename", 'r', \$recv );
run io( \*HANDLE, 'r', \$recv );
DESCRIPTION
IPC::Run allows you to run and interact with child processes using
files, pipes, and pseudo-ttys. Both system()-style and scripted usages
are supported and may be mixed. Likewise, functional and OO API styles
are both supported and may be mixed.
Various redirection operators reminiscent of those seen on common Unix
and DOS command lines are provided.
Before digging in to the details a few LIMITATIONS are important enough
to be mentioned right up front:
Win32 Support
Win32 support is working but EXPERIMENTAL, but does pass all
relevant tests on NT 4.0. See "Win32 LIMITATIONS".
pty Support
If you need pty support, IPC::Run should work well enough most of
the time, but IO::Pty is being improved, and IPC::Run will be
improved to use IO::Pty's new features when it is released.
The basic problem is that the pty needs to initialize itself before
the parent writes to the master pty, or the data written gets lost.
So IPC::Run does a sleep(1) in the parent after forking to
(hopefully) give the child a chance to run. This is a kludge that
works well on non heavily loaded systems :(.
ptys are not supported yet under Win32, but will be emulated...
Debugging Tip
You may use the environment variable "IPCRUNDEBUG" to see what's
going on under the hood:
$ IPCRUNDEBUG=basic myscript # prints minimal debugging
$ IPCRUNDEBUG=data myscript # prints all data reads/writes
$ IPCRUNDEBUG=details myscript # prints lots of low-level details
$ IPCRUNDEBUG=gory myscript # (Win32 only) prints data moving through
# the helper processes.
We now return you to your regularly scheduled documentation.
Harnesses
Child processes and I/O handles are gathered in to a harness, then
started and run until the processing is finished or aborted.
run() vs. start(); pump(); finish();
There are two modes you can run harnesses in: run() functions as an
enhanced system(), and start()/pump()/finish() allow for background
processes and scripted interactions with them.
When using run(), all data to be sent to the harness is set up in
advance (though one can feed subprocesses input from subroutine refs to
get around this limitation). The harness is run and all output is
collected from it, then any child processes are waited for:
run \@cmd, \<<IN, \$out;
blah
IN
## To precompile harnesses and run them later:
my $h = harness \@cmd, \<<IN, \$out;
blah
IN
run $h;
The background and scripting API is provided by start(), pump(), and
finish(): start() creates a harness if need be (by calling harness())
and launches any subprocesses, pump() allows you to poll them for
activity, and finish() then monitors the harnessed activities until they
complete.
## Build the harness, open all pipes, and launch the subprocesses
my $h = start \@cat, \$in, \$out;
$in = "first input\n";
## Now do I/O. start() does no I/O.
pump $h while length $in; ## Wait for all input to go
## Now do some more I/O.
$in = "second input\n";
pump $h until $out =~ /second input/;
## Clean up
finish $h or die "cat returned $?";
You can optionally compile the harness with harness() prior to
start()ing or run()ing, and you may omit start() between harness() and
pump(). You might want to do these things if you compile your harnesses
ahead of time.
Using regexps to match output
As shown in most of the scripting examples, the read-to-scalar facility
for gathering subcommand's output is often used with regular expressions
to detect stopping points. This is because subcommand output often
arrives in dribbles and drabs, often only a character or line at a time.
This output is input for the main program and piles up in variables like
the $out and $err in our examples.
Regular expressions can be used to wait for appropriate output in
several ways. The "cat" example in the previous section demonstrates
how to pump() until some string appears in the output. Here's an
example that uses "smb" to fetch files from a remote server:
$h = harness \@smbclient, \$in, \$out;
$in = "cd /src\n";
$h->pump until $out =~ /^smb.*> \Z/m;
die "error cding to /src:\n$out" if $out =~ "ERR";
$out = '';
$in = "mget *\n";
$h->pump until $out =~ /^smb.*> \Z/m;
die "error retrieving files:\n$out" if $out =~ "ERR";
$in = "quit\n";
$h->finish;
Notice that we carefully clear $out after the first command/response
cycle? That's because IPC::Run does not delete $out when we continue,
and we don't want to trip over the old output in the second
command/response cycle.
Say you want to accumulate all the output in $out and analyze it
afterwards. Perl offers incremental regular expression matching using
the "m//gc" and pattern matching idiom and the "\G" assertion. IPC::Run
is careful not to disturb the current pos() value for scalars it appends
data to, so we could modify the above so as not to destroy $out by
adding a couple of "/gc" modifiers. The "/g" keeps us from tripping
over the previous prompt and the "/c" keeps us from resetting the prior
match position if the expected prompt doesn't materialize immediately:
$h = harness \@smbclient, \$in, \$out;
$in = "cd /src\n";
$h->pump until $out =~ /^smb.*> \Z/mgc;
die "error cding to /src:\n$out" if $out =~ "ERR";
$in = "mget *\n";
$h->pump until $out =~ /^smb.*> \Z/mgc;
die "error retrieving files:\n$out" if $out =~ "ERR";
$in = "quit\n";
$h->finish;
analyze( $out );
When using this technique, you may want to preallocate $out to have
plenty of memory or you may find that the act of growing $out each time
new input arrives causes an "O(length($out)^2)" slowdown as $out grows.
Say we expect no more than 10,000 characters of input at the most. To
preallocate memory to $out, do something like:
my $out = "x" x 10_000;
$out = "";
"perl" will allocate at least 10,000 characters' worth of space, then
mark the $out as having 0 length without freeing all that yummy RAM.
Timeouts and Timers
More than likely, you don't want your subprocesses to run forever, and
sometimes it's nice to know that they're going a little slowly.
Timeouts throw exceptions after a some time has elapsed, timers merely
cause pump() to return after some time has elapsed. Neither is
reset/restarted automatically.
Timeout objects are created by calling timeout( $interval ) and passing
the result to run(), start() or harness(). The timeout period starts
ticking just after all the child processes have been fork()ed or
spawn()ed, and are polled for expiration in run(), pump() and finish().
If/when they expire, an exception is thrown. This is typically useful
to keep a subprocess from taking too long.
If a timeout occurs in run(), all child processes will be terminated and
all file/pipe/ptty descriptors opened by run() will be closed. File
descriptors opened by the parent process and passed in to run() are not
closed in this event.
If a timeout occurs in pump(), pump_nb(), or finish(), it's up to you to
decide whether to kill_kill() all the children or to implement some more
graceful fallback. No I/O will be closed in pump(), pump_nb() or
finish() by such an exception (though I/O is often closed down in those
routines during the natural course of events).
Often an exception is too harsh. timer( $interval ) creates timer
objects that merely prevent pump() from blocking forever. This can be
useful for detecting stalled I/O or printing a soothing message or "."
to pacify an anxious user.
Timeouts and timers can both be restarted at any time using the timer's
start() method (this is not the start() that launches subprocesses). To
restart a timer, you need to keep a reference to the timer:
## Start with a nice long timeout to let smbclient connect. If
## pump or finish take too long, an exception will be thrown.
my $h;
eval {
$h = harness \@smbclient, \$in, \$out, \$err, ( my $t = timeout 30 );
sleep 11; # No effect: timer not running yet
start $h;
$in = "cd /src\n";
pump $h until ! length $in;
$in = "ls\n";
## Now use a short timeout, since this should be faster
$t->start( 5 );
pump $h until ! length $in;
$t->start( 10 ); ## Give smbclient a little while to shut down.
$h->finish;
};
if ( $@ ) {
my $x = $@; ## Preserve $@ in case another exception occurs
$h->kill_kill; ## kill it gently, then brutally if need be, or just
## brutally on Win32.
die $x;
}
Timeouts and timers are not checked once the subprocesses are shut down;
they will not expire in the interval between the last valid process and
when IPC::Run scoops up the processes' result codes, for instance.
Spawning synchronization, child exception propagation
start() pauses the parent until the child executes the command or CODE
reference and propagates any exceptions thrown (including exec()
failure) back to the parent. This has several pleasant effects: any
exceptions thrown in the child, including exec() failure, come flying
out of start() or run() as though they had occurred in the parent.
This includes exceptions your code thrown from init subs. In this
example:
eval {
run \@cmd, init => sub { die "blast it! foiled again!" };
};
print $@;
the exception "blast it! foiled again" will be thrown from the child
process (preventing the exec()) and printed by the parent.
In situations like
run \@cmd1, "|", \@cmd2, "|", \@cmd3;
@cmd1 will be initted and exec()ed before @cmd2, and @cmd2 before @cmd3.
This can save time and prevent oddball errors emitted by later commands
when earlier commands fail to execute. Note that IPC::Run doesn't start
any commands unless it can find the executables referenced by all
commands. These executables must pass both the "-f" and "-x" tests
described in perlfunc.
Another nice effect is that init() subs can take their time doing things
and there will be no problems caused by a parent continuing to execute
before a child's init() routine is complete. Say the init() routine
needs to open a socket or a temp file that the parent wants to connect
to; without this synchronization, the parent will need to implement a
retry loop to wait for the child to run, since often, the parent gets a
lot of things done before the child's first timeslice is allocated.
This is also quite necessary for pseudo-tty initialization, which needs
to take place before the parent writes to the child via pty. Writes
that occur before the pty is set up can get lost.
A final, minor, nicety is that debugging output from the child will be
emitted before the parent continues on, making for much clearer
debugging output in complex situations.
The only drawback I can conceive of is that the parent can't continue to
operate while the child is being initted. If this ever becomes a
problem in the field, we can implement an option to avoid this behavior,
but I don't expect it to.
Win32: executing CODE references isn't supported on Win32, see "Win32
LIMITATIONS" for details.
Syntax
run(), start(), and harness() can all take a harness specification as
input. A harness specification is either a single string to be passed
to the systems' shell:
run "echo 'hi there'";
or a list of commands, io operations, and/or timers/timeouts to execute.
Consecutive commands must be separated by a pipe operator '|' or an '&'.
External commands are passed in as array references or
IPC::Run::Win32Process objects. On systems supporting fork(), Perl code
may be passed in as subs:
run \@cmd;
run \@cmd1, '|', \@cmd2;
run \@cmd1, '&', \@cmd2;
run \&sub1;
run \&sub1, '|', \&sub2;
run \&sub1, '&', \&sub2;
'|' pipes the stdout of \@cmd1 the stdin of \@cmd2, just like a shell
pipe. '&' does not. Child processes to the right of a '&' will have
their stdin closed unless it's redirected-to.
IPC::Run::IO objects may be passed in as well, whether or not child
processes are also specified:
run io( "infile", ">", \$in ), io( "outfile", "<", \$in );
as can IPC::Run::Timer objects:
run \@cmd, io( "outfile", "<", \$in ), timeout( 10 );
Commands may be followed by scalar, sub, or i/o handle references for
redirecting child process input & output:
run \@cmd, \undef, \$out;
run \@cmd, \$in, \$out;
run \@cmd1, \&in, '|', \@cmd2, \*OUT;
run \@cmd1, \*IN, '|', \@cmd2, \&out;
This is known as succinct redirection syntax, since run(), start() and
harness(), figure out which file descriptor to redirect and how. File
descriptor 0 is presumed to be an input for the child process, all
others are outputs. The assumed file descriptor always starts at 0,
unless the command is being piped to, in which case it starts at 1.
To be explicit about your redirects, or if you need to do more complex
things, there's also a redirection operator syntax:
run \@cmd, '<', \undef, '>', \$out;
run \@cmd, '<', \undef, '>&', \$out_and_err;
run(
\@cmd1,
'<', \$in,
'|', \@cmd2,
\$out
);
Operator syntax is required if you need to do something other than
simple redirection to/from scalars or subs, like duping or closing file
descriptors or redirecting to/from a named file. The operators are
covered in detail below.
After each \@cmd (or \&foo), parsing begins in succinct mode and toggles
to operator syntax mode when an operator (ie plain scalar, not a ref) is
seen. Once in operator syntax mode, parsing only reverts to succinct
mode when a '|' or '&' is seen.
In succinct mode, each parameter after the \@cmd specifies what to do
with the next highest file descriptor. These File descriptor start with
0 (stdin) unless stdin is being piped to ("'|', \@cmd"), in which case
they start with 1 (stdout). Currently, being on the left of a pipe
("\@cmd, \$out, \$err, '|'") does not cause stdout to be skipped, though
this may change since it's not as DWIMerly as it could be. Only stdin
is assumed to be an input in succinct mode, all others are assumed to be
outputs.
If no piping or redirection is specified for a child, it will inherit
the parent's open file handles as dictated by your system's close-on-
exec behavior and the $^F flag, except that processes after a '&' will
not inherit the parent's stdin. Also note that $^F does not affect file
descriptors obtained via POSIX, since it only applies to full-fledged
Perl file handles. Such processes will have their stdin closed unless
it has been redirected-to.
If you want to close a child processes stdin, you may do any of:
run \@cmd, \undef;
run \@cmd, \"";
run \@cmd, '<&-';
run \@cmd, '0<&-';
Redirection is done by placing redirection specifications immediately
after a command or child subroutine:
run \@cmd1, \$in, '|', \@cmd2, \$out;
run \@cmd1, '<', \$in, '|', \@cmd2, '>', \$out;
If you omit the redirection operators, descriptors are counted starting
at 0. Descriptor 0 is assumed to be input, all others are outputs. A
leading '|' consumes descriptor 0, so this works as expected.
run \@cmd1, \$in, '|', \@cmd2, \$out;
The parameter following a redirection operator can be a scalar ref, a
subroutine ref, a file name, an open filehandle, or a closed filehandle.
If it's a scalar ref, the child reads input from or sends output to that
variable:
$in = "Hello World.\n";
run \@cat, \$in, \$out;
print $out;
Scalars used in incremental (start()/pump()/finish()) applications are
treated as queues: input is removed from input scalars, resulting in
them dwindling to '', and output is appended to output scalars. This is
not true of harnesses run() in batch mode.
It's usually wise to append new input to be sent to the child to the
input queue, and you'll often want to zap output queues to '' before
pumping.
$h = start \@cat, \$in;
$in = "line 1\n";
pump $h;
$in .= "line 2\n";
pump $h;
$in .= "line 3\n";
finish $h;
The final call to finish() must be there: it allows the child
process(es) to run to completion and waits for their exit values.
OBSTINATE CHILDREN
Interactive applications are usually optimized for human use. This can
help or hinder trying to interact with them through modules like
IPC::Run. Frequently, programs alter their behavior when they detect
that stdin, stdout, or stderr are not connected to a tty, assuming that
they are being run in batch mode. Whether this helps or hurts depends
on which optimizations change. And there's often no way of telling what
a program does in these areas other than trial and error and
occasionally, reading the source. This includes different versions and
implementations of the same program.
All hope is not lost, however. Most programs behave in reasonably
tractable manners, once you figure out what it's trying to do.
Here are some of the issues you might need to be aware of.
• fflush()ing stdout and stderr
This lets the user see stdout and stderr immediately. Many programs
undo this optimization if stdout is not a tty, making them harder to
manage by things like IPC::Run.
Many programs decline to fflush stdout or stderr if they do not
detect a tty there. Some ftp commands do this, for instance.
If this happens to you, look for a way to force interactive
behavior, like a command line switch or command. If you can't, you
will need to use a pseudo terminal ('<pty<' and '>pty>').
• false prompts
Interactive programs generally do not guarantee that output from
user commands won't contain a prompt string. For example, your
shell prompt might be a '$', and a file named '$' might be the only
file in a directory listing.
This can make it hard to guarantee that your output parser won't be
fooled into early termination of results.
To help work around this, you can see if the program can alter it's
prompt, and use something you feel is never going to occur in actual
practice.
You should also look for your prompt to be the only thing on a line:
pump $h until $out =~ /^<SILLYPROMPT>\s?\z/m;
(use "(?!\n)\Z" in place of "\z" on older perls).
You can also take the approach that IPC::ChildSafe takes and emit a
command with known output after each 'real' command you issue, then
look for this known output. See new_appender() and new_chunker()
for filters that can help with this task.
If it's not convenient or possibly to alter a prompt or use a known
command/response pair, you might need to autodetect the prompt in
case the local version of the child program is different then the
one you tested with, or if the user has control over the look & feel
of the prompt.
• Refusing to accept input unless stdin is a tty.
Some programs, for security reasons, will only accept certain types
of input from a tty. su, notable, will not prompt for a password
unless it's connected to a tty.
If this is your situation, use a pseudo terminal ('<pty<' and
'>pty>').
• Not prompting unless connected to a tty.
Some programs don't prompt unless stdin or stdout is a tty. See if
you can turn prompting back on. If not, see if you can come up with
a command that you can issue after every real command and look for
it's output, as IPC::ChildSafe does. There are two filters
included with IPC::Run that can help with doing this: appender and
chunker (see new_appender() and new_chunker()).
• Different output format when not connected to a tty.
Some commands alter their formats to ease machine parsability when
they aren't connected to a pipe. This is actually good, but can be
surprising.
PSEUDO TERMINALS
On systems providing pseudo terminals under /dev, IPC::Run can use
IO::Pty (available on CPAN) to provide a terminal environment to
subprocesses. This is necessary when the subprocess really wants to
think it's connected to a real terminal.
CAVEATS
Pseudo-terminals are not pipes, though they are similar. Here are some
differences to watch out for.
Echoing
Sending to stdin will cause an echo on stdout, which occurs before
each line is passed to the child program. There is currently no way
to disable this, although the child process can and should disable
it for things like passwords.
Shutdown
IPC::Run cannot close a pty until all output has been collected.
This means that it is not possible to send an EOF to stdin by half-
closing the pty, as we can when using a pipe to stdin.
This means that you need to send the child process an exit command
or signal, or run() / finish() will time out. Be careful not to
expect a prompt after sending the exit command.
Command line editing
Some subprocesses, notable shells that depend on the user's prompt
settings, will reissue the prompt plus the command line input so far
once for each character.
'>pty>' means '&>pty>', not '1>pty>'
The pseudo terminal redirects both stdout and stderr unless you
specify a file descriptor. If you want to grab stderr separately,
do this:
start \@cmd, '<pty<', \$in, '>pty>', \$out, '2>', \$err;
stdin, stdout, and stderr not inherited
Child processes harnessed to a pseudo terminal have their stdin,
stdout, and stderr completely closed before any redirection
operators take effect. This casts off the bonds of the controlling
terminal. This is not done when using pipes.
Right now, this affects all children in a harness that has a pty in
use, even if that pty would not affect a particular child. That's a
bug and will be fixed. Until it is, it's best not to mix-and-match
children.
Redirection Operators
Operator SHNP Description
======== ==== ===========
<, N< SHN Redirects input to a child's fd N (0 assumed)
>, N> SHN Redirects output from a child's fd N (1 assumed)
>>, N>> SHN Like '>', but appends to scalars or named files
>&, &> SHN Redirects stdout & stderr from a child process
<pty, N<pty S Like '<', but uses a pseudo-tty instead of a pipe
>pty, N>pty S Like '>', but uses a pseudo-tty instead of a pipe
N<&M Dups input fd N to input fd M
M>&N Dups output fd N to input fd M
N<&- Closes fd N
<pipe, N<pipe P Pipe opens H for caller to read, write, close.
>pipe, N>pipe P Pipe opens H for caller to read, write, close.
'N' and 'M' are placeholders for integer file descriptor numbers. The
terms 'input' and 'output' are from the child process's perspective.
The SHNP field indicates what parameters an operator can take:
S: \$scalar or \&function references. Filters may be used with
these operators (and only these).
H: \*HANDLE or IO::Handle for caller to open, and close
N: "file name".
P: \*HANDLE or lexical filehandle opened by IPC::Run as the parent end of a pipe, but read
and written to and closed by the caller (like IPC::Open3).
Redirecting input: [n]<, [n]<pipe
You can input the child reads on file descriptor number n to come
from a scalar variable, subroutine, file handle, or a named file.
If stdin is not redirected, the parent's stdin is inherited.
run \@cat, \undef ## Closes child's stdin immediately
or die "cat returned $?";
run \@cat, \$in;
run \@cat, \<<TOHERE;
blah
TOHERE
run \@cat, \&input; ## Calls &input, feeding data returned
## to child's. Closes child's stdin
## when undef is returned.
Redirecting from named files requires you to use the input
redirection operator:
run \@cat, '<.profile';
run \@cat, '<', '.profile';
open IN, "<foo";
run \@cat, \*IN;
run \@cat, *IN{IO};
The form used second example here is the safest, since filenames
like "0" and "&more\n" won't confuse &run:
You can't do either of
run \@a, *IN; ## INVALID
run \@a, '<', *IN; ## BUGGY: Reads file named like "*main::A"
because perl passes a scalar containing a string that looks like
"*main::A" to &run, and &run can't tell the difference between that
and a redirection operator or a file name. &run guarantees that any
scalar you pass after a redirection operator is a file name.
If your child process will take input from file descriptors other
than 0 (stdin), you can use a redirection operator with any of the
valid input forms (scalar ref, sub ref, etc.):
run \@cat, '3<', \$in3;
When redirecting input from a scalar ref, the scalar ref is used as
a queue. This allows you to use &harness and pump() to feed
incremental bits of input to a coprocess. See "Coprocesses" below
for more information.
The <pipe operator opens the write half of a pipe on the filehandle
glob reference it takes as an argument:
$h = start \@cat, '<pipe', \*IN;
print IN "hello world\n";
pump $h;
close IN;
finish $h;
Unlike the other '<' operators, IPC::Run does nothing further with
it: you are responsible for it. The previous example is
functionally equivalent to:
pipe( \*R, \*IN ) or die $!;
$h = start \@cat, '<', \*IN;
print IN "hello world\n";
pump $h;
close IN;
finish $h;
This is like the behavior of IPC::Open2 and IPC::Open3.
Win32: The handle returned is actually a socket handle, so you can
use select() on it.
Redirecting output: [n]>, [n]>>, [n]>&[m], [n]>pipe
You can redirect any output the child emits to a scalar variable,
subroutine, file handle, or file name. You can have &run truncate
or append to named files or scalars. If you are redirecting stdin
as well, or if the command is on the receiving end of a pipeline
('|'), you can omit the redirection operator:
@ls = ( 'ls' );
run \@ls, \undef, \$out
or die "ls returned $?";
run \@ls, \undef, \&out; ## Calls &out each time some output
## is received from the child's
## when undef is returned.
run \@ls, \undef, '2>ls.err';
run \@ls, '2>', 'ls.err';
The two parameter form guarantees that the filename will not be
interpreted as a redirection operator:
run \@ls, '>', "&more";
run \@ls, '2>', ">foo\n";
You can pass file handles you've opened for writing:
open( *OUT, ">out.txt" );
open( *ERR, ">err.txt" );
run \@cat, \*OUT, \*ERR;
Passing a scalar reference and a code reference requires a little
more work, but allows you to capture all of the output in a scalar
or each piece of output by a callback:
These two do the same things:
run( [ 'ls' ], '2>', sub { $err_out .= $_[0] } );
does the same basic thing as:
run( [ 'ls' ], '2>', \$err_out );
The subroutine will be called each time some data is read from the
child.
The >pipe operator is different in concept than the other '>'
operators, although it's syntax is similar:
$h = start \@cat, $in, '>pipe', \*OUT, '2>pipe', \*ERR;
$in = "hello world\n";
finish $h;
print <OUT>;
print <ERR>;
close OUT;
close ERR;
causes two pipe to be created, with one end attached to cat's stdout
and stderr, respectively, and the other left open on OUT and ERR, so
that the script can manually read(), select(), etc. on them. This
is like the behavior of IPC::Open2 and IPC::Open3.
Win32: The handle returned is actually a socket handle, so you can
use select() on it.
Duplicating output descriptors: >&m, n>&m
This duplicates output descriptor number n (default is 1 if n is
omitted) from descriptor number m.
Duplicating input descriptors: <&m, n<&m
This duplicates input descriptor number n (default is 0 if n is
omitted) from descriptor number m
Closing descriptors: <&-, 3<&-
This closes descriptor number n (default is 0 if n is omitted). The
following commands are equivalent:
run \@cmd, \undef;
run \@cmd, '<&-';
run \@cmd, '<in.txt', '<&-';
Doing
run \@cmd, \$in, '<&-'; ## SIGPIPE recipe.
is dangerous: the parent will get a SIGPIPE if $in is not empty.
Redirecting both stdout and stderr: &>, >&, &>pipe, >pipe&
The following pairs of commands are equivalent:
run \@cmd, '>&', \$out; run \@cmd, '>', \$out, '2>&1';
run \@cmd, '>&', 'out.txt'; run \@cmd, '>', 'out.txt', '2>&1';
etc.
File descriptor numbers are not permitted to the left or the right
of these operators, and the '&' may occur on either end of the
operator.
The '&>pipe' and '>pipe&' variants behave like the '>pipe' operator,
except that both stdout and stderr write to the created pipe.
Redirection Filters
Both input redirections and output redirections that use scalars or
subs as endpoints may have an arbitrary number of filter subs placed
between them and the child process. This is useful if you want to
receive output in chunks, or if you want to massage each chunk of
data sent to the child. To use this feature, you must use operator
syntax:
run(
\@cmd
'<', \&in_filter_2, \&in_filter_1, $in,
'>', \&out_filter_1, \&in_filter_2, $out,
);
This capability is not provided for IO handles or named files.
Two filters are provided by IPC::Run: appender and chunker. Because
these may take an argument, you need to use the constructor
functions new_appender() and new_chunker() rather than using \&
syntax:
run(
\@cmd
'<', new_appender( "\n" ), $in,
'>', new_chunker, $out,
);
Just doing I/O
If you just want to do I/O to a handle or file you open yourself, you
may specify a filehandle or filename instead of a command in the harness
specification:
run io( "filename", '>', \$recv );
$h = start io( $io, '>', \$recv );
$h = harness \@cmd, '&', io( "file", '<', \$send );
Options
Options are passed in as name/value pairs:
run \@cat, \$in, debug => 1;
If you pass the debug option, you may want to pass it in first, so you
can see what parsing is going on:
run debug => 1, \@cat, \$in;
debug
Enables debugging output in parent and child. Debugging info is
emitted to the STDERR that was present when IPC::Run was first
use()ed (it's dup()ed out of the way so that it can be redirected in
children without having debugging output emitted on it).
RETURN VALUES
harness() and start() return a reference to an IPC::Run harness. This
is blessed in to the IPC::Run package, so you may make later calls to
functions as members if you like:
$h = harness( ... );
$h->start;
$h->pump;
$h->finish;
$h = start( .... );
$h->pump;
...
Of course, using method call syntax lets you deal with any IPC::Run
subclasses that might crop up, but don't hold your breath waiting for
any.
run() and finish() return TRUE when all subcommands exit with a 0 result
code. This is the opposite of perl's system() command.
All routines raise exceptions (via die()) when error conditions are
recognized. A non-zero command result is not treated as an error
condition, since some commands are tests whose results are reported in
their exit codes.
ROUTINES
run Run takes a harness or harness specification and runs it,
pumping all input to the child(ren), closing the input pipes
when no more input is available, collecting all output that
arrives, until the pipes delivering output are closed, then
waiting for the children to exit and reaping their result codes.
You may think of run( ... ) as being like
start( ... )->finish();
, though there is one subtle difference: run() does not set
\$input_scalars to '' like finish() does. If an exception is
thrown from run(), all children will be killed off "gently", and
then "annihilated" if they do not go gently (in to that dark
night. sorry).
If any exceptions are thrown, this does a "kill_kill" before
propagating them.
signal
## To send it a specific signal by name ("USR1"):
signal $h, "USR1";
$h->signal ( "USR1" );
If $signal is provided and defined, sends a signal to all child
processes. Try not to send numeric signals, use "KILL" instead
of 9, for instance. Numeric signals aren't portable.
Throws an exception if $signal is undef.
This will not clean up the harness, "finish" it if you kill it.
Normally TERM kills a process gracefully (this is what the
command line utility "kill" does by default), INT is sent by one
of the keys "^C", "Backspace" or "<Del>", and "QUIT" is used to
kill a process and make it coredump.
The "HUP" signal is often used to get a process to "restart",
rereading config files, and "USR1" and "USR2" for really
application-specific things.
Often, running "kill -l" (that's a lower case "L") on the
command line will list the signals present on your operating
system.
WARNING: The signal subsystem is not at all portable. We *may*
offer to simulate "TERM" and "KILL" on some operating systems,
submit code to me if you want this.
WARNING 2: Up to and including perl v5.6.1, doing almost
anything in a signal handler could be dangerous. The most safe
code avoids all mallocs and system calls, usually by
preallocating a flag before entering the signal handler,
altering the flag's value in the handler, and responding to the
changed value in the main system:
my $got_usr1 = 0;
sub usr1_handler { ++$got_signal }
$SIG{USR1} = \&usr1_handler;
while () { sleep 1; print "GOT IT" while $got_usr1--; }
Even this approach is perilous if ++ and -- aren't atomic on
your system (I've never heard of this on any modern CPU large
enough to run perl).
kill_kill
## To kill off a process:
$h->kill_kill;
kill_kill $h;
## To specify the grace period other than 30 seconds:
kill_kill $h, grace => 5;
## To send QUIT instead of KILL if a process refuses to die:
kill_kill $h, coup_d_grace => "QUIT";
Sends a "TERM", waits for all children to exit for up to 30
seconds, then sends a "KILL" to any that survived the "TERM".
Will wait for up to 30 more seconds for the OS to successfully
"KILL" the processes.
The 30 seconds may be overridden by setting the "grace" option,
this overrides both timers.
The harness is then cleaned up.
The doubled name indicates that this function may kill again and
avoids colliding with the core Perl "kill" function.
Returns a 1 if the "TERM" was sufficient, or a 0 if "KILL" was
required. Throws an exception if "KILL" did not permit the
children to be reaped.
NOTE: The grace period is actually up to 1 second longer than
that given. This is because the granularity of "time" is 1
second. Let me know if you need finer granularity, we can
leverage Time::HiRes here.
Win32: Win32 does not know how to send real signals, so "TERM"
is a full-force kill on Win32. Thus all talk of grace periods,
etc. do not apply to Win32.
harness
Takes a harness specification and returns a harness. This
harness is blessed in to IPC::Run, allowing you to use method
call syntax for run(), start(), et al if you like.
harness() is provided so that you can pre-build harnesses if you
would like to, but it's not required..
You may proceed to run(), start() or pump() after calling
harness() (pump() calls start() if need be). Alternatively, you
may pass your harness specification to run() or start() and let
them harness() for you. You can't pass harness specifications
to pump(), though.
close_terminal
This is used as (or in) an init sub to cast off the bonds of a
controlling terminal. It must precede all other redirection ops
that affect STDIN, STDOUT, or STDERR to be guaranteed effective.
start
$h = start(
\@cmd, \$in, \$out, ...,
timeout( 30, name => "process timeout" ),
$stall_timeout = timeout( 10, name => "stall timeout" ),
);
$h = start \@cmd, '<', \$in, '|', \@cmd2, ...;
start() accepts a harness or harness specification and returns a
harness after building all of the pipes and launching (via
fork()/exec(), or, maybe someday, spawn()) all the child
processes. It does not send or receive any data on the pipes,
see pump() and finish() for that.
You may call harness() and then pass it's result to start() if
you like, but you only need to if it helps you structure or tune
your application. If you do call harness(), you may skip
start() and proceed directly to pump.
start() also starts all timers in the harness. See
IPC::Run::Timer for more information.
start() flushes STDOUT and STDERR to help you avoid duplicate
output. It has no way of asking Perl to flush all your open
filehandles, so you are going to need to flush any others you
have open. Sorry.
Here's how if you don't want to alter the state of $| for your
filehandle:
$ofh = select HANDLE; $of = $|; $| = 1; $| = $of; select $ofh;
If you don't mind leaving output unbuffered on HANDLE, you can
do the slightly shorter
$ofh = select HANDLE; $| = 1; select $ofh;
Or, you can use IO::Handle's flush() method:
use IO::Handle;
flush HANDLE;
Perl needs the equivalent of C's fflush( (FILE *)NULL ).
adopt
Experimental feature. NOT FUNCTIONAL YET, NEED TO CLOSE FDS
BETTER IN CHILDREN. SEE t/adopt.t for a test suite.
pump
pump $h;
$h->pump;
Pump accepts a single parameter harness. It blocks until it
delivers some input or receives some output. It returns TRUE if
there is still input or output to be done, FALSE otherwise.
pump() will automatically call start() if need be, so you may
call harness() then proceed to pump() if that helps you
structure your application.
If pump() is called after all harnessed activities have
completed, a "process ended prematurely" exception to be thrown.
This allows for simple scripting of external applications
without having to add lots of error handling code at each step
of the script:
$h = harness \@smbclient, \$in, \$out, $err;
$in = "cd /foo\n";
$h->pump until $out =~ /^smb.*> \Z/m;
die "error cding to /foo:\n$out" if $out =~ "ERR";
$out = '';
$in = "mget *\n";
$h->pump until $out =~ /^smb.*> \Z/m;
die "error retrieving files:\n$out" if $out =~ "ERR";
$h->finish;
warn $err if $err;
pump_nb
pump_nb $h;
$h->pump_nb;
"pump() non-blocking", pumps if anything's ready to be pumped,
returns immediately otherwise. This is useful if you're doing
some long-running task in the foreground, but don't want to
starve any child processes.
pumpable
Returns TRUE if calling pump() won't throw an immediate "process
ended prematurely" exception. This means that there are open
I/O channels or active processes. May yield the parent
processes' time slice for 0.01 second if all pipes are to the
child and all are paused. In this case we can't tell if the
child is dead, so we yield the processor and then attempt to
reap the child in a nonblocking way.
reap_nb
Attempts to reap child processes, but does not block.
Does not currently take any parameters, one day it will allow
specific children to be reaped.
Only call this from a signal handler if your "perl" is recent
enough to have safe signal handling (5.6.1 did not, IIRC, but it
was being discussed on perl5-porters). Calling this (or doing
any significant work) in a signal handler on older "perl"s is
asking for seg faults.
finish
This must be called after the last start() or pump() call for a
harness, or your system will accumulate defunct processes and
you may "leak" file descriptors.
finish() returns TRUE if all children returned 0 (and were not
signaled and did not coredump, ie ! $?), and FALSE otherwise
(this is like run(), and the opposite of system()).
Once a harness has been finished, it may be run() or start()ed
again, including by pump()s auto-start.
If this throws an exception rather than a normal exit, the
harness may be left in an unstable state, it's best to kill the
harness to get rid of all the child processes, etc.
Specifically, if a timeout expires in finish(), finish() will
not kill all the children. Call "$h->kill_kill" in this case if
you care. This differs from the behavior of "run".
result
$h->result;
Returns the first non-zero result code (ie $? >> 8). See
"full_result" to get the $? value for a child process.
To get the result of a particular child, do:
$h->result( 0 ); # first child's $? >> 8
$h->result( 1 ); # second child
or
($h->results)[0]
($h->results)[1]
Returns undef if no child processes were spawned and no child
number was specified. Throws an exception if an out-of-range
child number is passed.
results
Returns a list of child exit values. See "full_results" if you
want to know if a signal killed the child.
Throws an exception if the harness is not in a finished state.
full_result
$h->full_result;
Returns the first non-zero $?. See "result" to get the first $?
>> 8 value for a child process.
To get the result of a particular child, do:
$h->full_result( 0 ); # first child's $?
$h->full_result( 1 ); # second child
or
($h->full_results)[0]
($h->full_results)[1]
Returns undef if no child processes were spawned and no child
number was specified. Throws an exception if an out-of-range
child number is passed.
full_results
Returns a list of child exit values as returned by "wait". See
"results" if you don't care about coredumps or signals.
Throws an exception if the harness is not in a finished state.
FILTERS
These filters are used to modify input our output between a child
process and a scalar or subroutine endpoint.
binary
run \@cmd, ">", binary, \$out;
run \@cmd, ">", binary, \$out; ## Any TRUE value to enable
run \@cmd, ">", binary 0, \$out; ## Any FALSE value to disable
This is a constructor for a "binmode" "filter" that tells IPC::Run
to keep the carriage returns that would ordinarily be edited out for
you (binmode is usually off). This is not a real filter, but an
option masquerading as a filter.
It's not named "binmode" because you're likely to want to call
Perl's binmode in programs that are piping binary data around.
new_chunker
This breaks a stream of data in to chunks, based on an optional
scalar or regular expression parameter. The default is the Perl
input record separator in $/, which is a newline be default.
run \@cmd, '>', new_chunker, \&lines_handler;
run \@cmd, '>', new_chunker( "\r\n" ), \&lines_handler;
Because this uses $/ by default, you should always pass in a
parameter if you are worried about other code (modules, etc)
modifying $/.
If this filter is last in a filter chain that dumps in to a scalar,
the scalar must be set to '' before a new chunk will be written to
it.
As an example of how a filter like this can be written, here's a
chunker that splits on newlines:
sub line_splitter {
my ( $in_ref, $out_ref ) = @_;
return 0 if length $$out_ref;
return input_avail && do {
while (1) {
if ( $$in_ref =~ s/\A(.*?\n)// ) {
$$out_ref .= $1;
return 1;
}
my $hmm = get_more_input;
unless ( defined $hmm ) {
$$out_ref = $$in_ref;
$$in_ref = '';
return length $$out_ref ? 1 : 0;
}
return 0 if $hmm eq 0;
}
}
};
new_appender
This appends a fixed string to each chunk of data read from the
source scalar or sub. This might be useful if you're writing
commands to a child process that always must end in a fixed string,
like "\n":
run( \@cmd,
'<', new_appender( "\n" ), \&commands,
);
Here's a typical filter sub that might be created by new_appender():
sub newline_appender {
my ( $in_ref, $out_ref ) = @_;
return input_avail && do {
$$out_ref = join( '', $$out_ref, $$in_ref, "\n" );
$$in_ref = '';
1;
}
};
new_string_source
TODO: Needs confirmation. Was previously undocumented. in this
module.
This is a filter which is exportable. Returns a sub which appends
the data passed in to the output buffer and returns 1 if data was
appended. 0 if it was an empty string and undef if no data was
passed.
NOTE: Any additional variables passed to new_string_source will be
passed to the sub every time it's called and appended to the output.
new_string_sink
TODO: Needs confirmation. Was previously undocumented.
This is a filter which is exportable. Returns a sub which pops the
data out of the input stream and pushes it onto the string.
io Takes a filename or filehandle, a redirection operator, optional
filters, and a source or destination (depends on the redirection
operator). Returns an IPC::Run::IO object suitable for harness()ing
(including via start() or run()).
This is shorthand for
require IPC::Run::IO;
... IPC::Run::IO->new(...) ...
timer
$h = start( \@cmd, \$in, \$out, $t = timer( 5 ) );
pump $h until $out =~ /expected stuff/ || $t->is_expired;
Instantiates a non-fatal timer. pump() returns once each time a
timer expires. Has no direct effect on run(), but you can pass a
subroutine to fire when the timer expires.
See "timeout" for building timers that throw exceptions on
expiration.
See "timer" in IPC::Run::Timer for details.
timeout
$h = start( \@cmd, \$in, \$out, $t = timeout( 5 ) );
pump $h until $out =~ /expected stuff/;
Instantiates a timer that throws an exception when it expires. If
you don't provide an exception, a default exception that matches
/^IPC::Run: .*timed out/ is thrown by default. You can pass in your
own exception scalar or reference:
$h = start(
\@cmd, \$in, \$out,
$t = timeout( 5, exception => 'slowpoke' ),
);
or set the name used in debugging message and in the default
exception string:
$h = start(
\@cmd, \$in, \$out,
timeout( 50, name => 'process timer' ),
$stall_timer = timeout( 5, name => 'stall timer' ),
);
pump $h until $out =~ /started/;
$in = 'command 1';
$stall_timer->start;
pump $h until $out =~ /command 1 finished/;
$in = 'command 2';
$stall_timer->start;
pump $h until $out =~ /command 2 finished/;
$in = 'very slow command 3';
$stall_timer->start( 10 );
pump $h until $out =~ /command 3 finished/;
$stall_timer->start( 5 );
$in = 'command 4';
pump $h until $out =~ /command 4 finished/;
$stall_timer->reset; # Prevent restarting or expirng
finish $h;
See "timer" for building non-fatal timers.
See "timer" in IPC::Run::Timer for details.
FILTER IMPLEMENTATION FUNCTIONS
These functions are for use from within filters.
input_avail
Returns TRUE if input is available. If none is available, then
&get_more_input is called and its result is returned.
This is usually used in preference to &get_more_input so that the
calling filter removes all data from the $in_ref before more data
gets read in to $in_ref.
"input_avail" is usually used as part of a return expression:
return input_avail && do {
## process the input just gotten
1;
};
This technique allows input_avail to return the undef or 0 that a
filter normally returns when there's no input to process. If a
filter stores intermediate values, however, it will need to react to
an undef:
my $got = input_avail;
if ( ! defined $got ) {
## No more input ever, flush internal buffers to $out_ref
}
return $got unless $got;
## Got some input, move as much as need be
return 1 if $added_to_out_ref;
get_more_input
This is used to fetch more input in to the input variable. It
returns undef if there will never be any more input, 0 if there is
none now, but there might be in the future, and TRUE if more input
was gotten.
"get_more_input" is usually used as part of a return expression, see
"input_avail" for more information.
TODO
These will be addressed as needed and as time allows.
Stall timeout.
Expose a list of child process objects. When I do this, each child
process is likely to be blessed into IPC::Run::Proc.
$kid->abort(), $kid->kill(), $kid->signal( $num_or_name ).
Write tests for /(full_)?results?/ subs.
Currently, pump() and run() only work on systems where select() works on
the filehandles returned by pipe(). This does *not* include ActiveState
on Win32, although it does work on cygwin under Win32 (thought the tests
whine a bit). I'd like to rectify that, suggestions and patches
welcome.
Likewise start() only fully works on fork()/exec() machines (well, just
fork() if you only ever pass perl subs as subprocesses). There's some
scaffolding for calling Open3::spawn_with_handles(), but that's
untested, and not that useful with limited select().
Support for "\@sub_cmd" as an argument to a command which gets replaced
with /dev/fd or the name of a temporary file containing foo's output.
This is like <(sub_cmd ...) found in bash and csh (IIRC).
Allow multiple harnesses to be combined as independent sets of processes
in to one 'meta-harness'.
Allow a harness to be passed in place of an \@cmd. This would allow
multiple harnesses to be aggregated.
Ability to add external file descriptors w/ filter chains and endpoints.
Ability to add timeouts and timing generators (i.e. repeating timeouts).
High resolution timeouts.
Win32 LIMITATIONS
argument-passing rules are program-specific
Win32 programs receive all arguments in a single "command line"
string. IPC::Run assembles this string so programs using standard
command line parsing rules <https://docs.microsoft.com/en-
us/cpp/cpp/main-function-command-line-args#parsing-c-command-line-
arguments> will see an "argv" that matches the array reference
specifying the command. Some programs use different rules to parse
their command line. Notable examples include cmd.exe, cscript.exe,
and Cygwin programs called from non-Cygwin programs. Use
IPC::Run::Win32Process to call these and other nonstandard programs.
batch files
Properly escaping a batch file argument depends on how the script
will use that argument, because some uses experience multiple levels
of caret (escape character) removal. Avoid calling batch files with
arguments, particularly when the argument values originate outside
your program or contain non-alphanumeric characters. Perl scripts
and PowerShell scripts are sound alternatives. If you do use batch
file arguments, IPC::Run escapes them so the batch file can pass
them, unquoted, to a program having standard command line parsing
rules. If the batch file enables delayed environment variable
expansion, it must disable that feature before expanding its
arguments. For example, if foo.cmd contains "perl %*", "run
['foo.cmd', @list]" will create a Perl process in which @ARGV
matches @list. Prepending a "setlocal enabledelayedexpansion" line
would make the batch file malfunction, silently. Another silent-
malfunction example is "run ['outer.bat', @list]" for outer.bat
containing "foo.cmd %*".
Fails on Win9X
If you want Win9X support, you'll have to debug it or fund me
because I don't use that system any more. The Win32 subsysem has
been extended to use temporary files in simple run() invocations and
these may actually work on Win9X too, but I don't have time to work
on it.
May deadlock on Win2K (but not WinNT4 or WinXPPro)
Spawning more than one subprocess on Win2K causes a deadlock I
haven't figured out yet, but simple uses of run() often work.
Passes all tests on WinXPPro and WinNT.
no support yet for <pty< and >pty>
These are likely to be implemented as "<" and ">" with binmode on,
not sure.
no support for file descriptors higher than 2 (stderr)
Win32 only allows passing explicit fds 0, 1, and 2. If you really,
really need to pass file handles, us Win32API:: GetOsFHandle() or
::FdGetOsFHandle() to get the integer handle and pass it to the
child process using the command line, environment, stdin,
intermediary file, or other IPC mechanism. Then use that handle in
the child (Win32API.pm provides ways to reconstitute Perl file
handles from Win32 file handles).
no support for subroutine subprocesses (CODE refs)
Can't fork(), so the subroutines would have no context, and closures
certainly have no meaning
Perhaps with Win32 fork() emulation, this can be supported in a
limited fashion, but there are other very serious problems with
that: all parent fds get dup()ed in to the thread emulating the
forked process, and that keeps the parent from being able to close
all of the appropriate fds.
no support for init => sub {} routines.
Win32 processes are created from scratch, there is no way to do an
init routine that will affect the running child. Some limited
support might be implemented one day, do chdir() and %ENV changes
can be made.
signals
Win32 does not fully support signals. signal() is likely to cause
errors unless sending a signal that Perl emulates, and kill_kill()
is immediately fatal (there is no grace period).
$? cannot represent all Win32 exit codes
Prefer full_result( ... ), result( ... ), or other IPC::Run methods.
helper processes
IPC::Run uses helper processes, one per redirected file, to adapt
between the anonymous pipe connected to the child and the TCP socket
connected to the parent. This is a waste of resources and will
change in the future to either use threads (instead of helper
processes) or a WaitForMultipleObjects call (instead of select).
Please contact me if you can help with the WaitForMultipleObjects()
approach; I haven't figured out how to get at it without C code.
shutdown pause
There seems to be a pause of up to 1 second between when a child
program exits and the corresponding sockets indicate that they are
closed in the parent. Not sure why.
binmode
binmode is not supported yet. The underpinnings are implemented,
just ask if you need it.
IPC::Run::IO
IPC::Run::IO objects can be used on Unix to read or write arbitrary
files. On Win32, they will need to use the same helper processes to
adapt from non-select()able filehandles to select()able ones (or
perhaps WaitForMultipleObjects() will work with them, not sure).
startup race conditions
There seems to be an occasional race condition between child process
startup and pipe closings. It seems like if the child is not fully
created by the time CreateProcess returns and we close the TCP
socket being handed to it, the parent socket can also get closed.
This is seen with the Win32 pumper applications, not the "real"
child process being spawned.
I assume this is because the kernel hasn't gotten around to
incrementing the reference count on the child's end (since the child
was slow in starting), so the parent's closing of the child end
causes the socket to be closed, thus closing the parent socket.
Being a race condition, it's hard to reproduce, but I encountered it
while testing this code on a drive share to a samba box. In this
case, it takes t/run.t a long time to spawn it's child processes
(the parent hangs in the first select for several seconds until the
child emits any debugging output).
I have not seen it on local drives, and can't reproduce it at will,
unfortunately. The symptom is a "bad file descriptor in select()"
error, and, by turning on debugging, it's possible to see that
select() is being called on a no longer open file descriptor that
was returned from the _socket() routine in Win32Helper. There's a
new confess() that checks for this ("PARENT_HANDLE no longer open"),
but I haven't been able to reproduce it (typically).
LIMITATIONS
On Unix, requires a system that supports "waitpid( $pid, WNOHANG )" so
it can tell if a child process is still running.
PTYs don't seem to be non-blocking on some versions of Solaris. Here's a
test script contributed by Borislav Deianov <borislav@ensim.com> to see
if you have the problem. If it dies, you have the problem.
#!/usr/bin/perl
use IPC::Run qw(run);
use Fcntl;
use IO::Pty;
sub makecmd {
return ['perl', '-e',
'<STDIN>, print "\n" x '.$_[0].'; while(<STDIN>){last if /end/}'];
}
#pipe R, W;
#fcntl(W, F_SETFL, O_NONBLOCK);
#while (syswrite(W, "\n", 1)) { $pipebuf++ };
#print "pipe buffer size is $pipebuf\n";
my $pipebuf=4096;
my $in = "\n" x ($pipebuf * 2) . "end\n";
my $out;
$SIG{ALRM} = sub { die "Never completed!\n" };
print "reading from scalar via pipe...";
alarm( 2 );
run(makecmd($pipebuf * 2), '<', \$in, '>', \$out);
alarm( 0 );
print "done\n";
print "reading from code via pipe... ";
alarm( 2 );
run(makecmd($pipebuf * 3), '<', sub { $t = $in; undef $in; $t}, '>', \$out);
alarm( 0 );
print "done\n";
$pty = IO::Pty->new();
$pty->blocking(0);
$slave = $pty->slave();
while ($pty->syswrite("\n", 1)) { $ptybuf++ };
print "pty buffer size is $ptybuf\n";
$in = "\n" x ($ptybuf * 3) . "end\n";
print "reading via pty... ";
alarm( 2 );
run(makecmd($ptybuf * 3), '<pty<', \$in, '>', \$out);
alarm(0);
print "done\n";
No support for ';', '&&', '||', '{ ... }', etc: use perl's, since run()
returns TRUE when the command exits with a 0 result code.
Does not provide shell-like string interpolation.
No support for "cd", "setenv", or "export": do these in an init() sub
run(
\cmd,
...
init => sub {
chdir $dir or die $!;
$ENV{FOO}='BAR'
}
);
Timeout calculation does not allow absolute times, or specification of
days, months, etc.
WARNING: Function coprocesses ("run \&foo, ...") suffer from two
limitations. The first is that it is difficult to close all filehandles
the child inherits from the parent, since there is no way to scan all
open FILEHANDLEs in Perl and it both painful and a bit dangerous to
close all open file descriptors with POSIX::close(). Painful because we
can't tell which fds are open at the POSIX level, either, so we'd have
to scan all possible fds and close any that we don't want open (normally
exec() closes any non-inheritable but we don't exec() for &sub
processes.
The second problem is that Perl's DESTROY subs and other on-exit cleanup
gets run in the child process. If objects are instantiated in the
parent before the child is forked, the DESTROY will get run once in the
parent and once in the child. When coprocess subs exit, POSIX::_exit is
called to work around this, but it means that objects that are still
referred to at that time are not cleaned up. So setting package vars or
closure vars to point to objects that rely on DESTROY to affect things
outside the process (files, etc), will lead to bugs.
I goofed on the syntax: "<pipe" vs. "<pty<" and ">filename" are both
oddities.
TODO
Allow one harness to "adopt" another:
$new_h = harness \@cmd2;
$h->adopt( $new_h );
Close all filehandles not explicitly marked to stay open.
The problem with this one is that there's no good way to scan all
open FILEHANDLEs in Perl, yet you don't want child processes
inheriting handles willy-nilly.
INSPIRATION
Well, select() and waitpid() badly needed wrapping, and open3() isn't
open-minded enough for me.
The shell-like API inspired by a message Russ Allbery sent to
perl5-porters, which included:
I've thought for some time that it would be
nice to have a module that could handle full Bourne shell pipe syntax
internally, with fork and exec, without ever invoking a shell. Something
that you could give things like:
pipeopen (PIPE, [ qw/cat file/ ], '|', [ 'analyze', @args ], '>&3');
Message ylln51p2b6.fsf@windlord.stanford.edu, on 2000/02/04.
SUPPORT
Bugs should always be submitted via the GitHub bug tracker
<https://github.com/toddr/IPC-Run/issues>
AUTHORS
Adam Kennedy <adamk@cpan.org>
Barrie Slaymaker <barries@slaysys.com>
COPYRIGHT
Some parts copyright 2008 - 2009 Adam Kennedy.
Copyright 1999 Barrie Slaymaker.
You may distribute under the terms of either the GNU General Public
License or the Artistic License, as specified in the README file.
perl v5.38.2 2024-04-01 IPC::Run(3pm)
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