LEXGROG(1) Manual pager utils LEXGROG(1)
NAME
lexgrog - parse header information in man pages
SYNOPSIS
lexgrog [-m|-c] [-dfw?V] [-E encoding] file ...
DESCRIPTION
lexgrog is an implementation of the traditional “groff guess” utility in
lex. It reads the list of files on its command line as either man page
source files or preformatted “cat” pages, and displays their name and
description as used by apropos and whatis, the list of preprocessing
filters required by the man page before it is passed to nroff or troff,
or both.
If its input is badly formatted, lexgrog will print “parse failed”; this
may be useful for external programs that need to check man pages for
correctness. If one of lexgrog's input files is “-”, it will read from
standard input; if any input file is compressed, a decompressed version
will be read automatically.
OPTIONS
-d, --debug
Print debugging information.
-m, --man
Parse input as man page source files. This is the default if
neither --man nor --cat is given.
-c, --cat
Parse input as preformatted man pages (“cat pages”). --man and
--cat may not be given simultaneously.
-w, --whatis
Display the name and description from the man page's header, as
used by apropos and whatis. This is the default if neither
--whatis nor --filters is given.
-f, --filters
Display the list of filters needed to preprocess the man page be-
fore formatting with nroff or troff.
-E encoding, --encoding encoding
Override the guessed character set for the page to encoding.
-?, --help
Print a help message and exit.
--usage
Print a short usage message and exit.
-V, --version
Display version information.
EXIT STATUS
0 Successful program execution.
1 Usage error.
2 lexgrog failed to parse one or more of its input files.
EXAMPLES
$ lexgrog man.1
man.1: "man - an interface to the system reference manuals"
$ lexgrog -fw man.1
man.1 (t): "man - an interface to the system reference manuals"
$ lexgrog -c whatis.cat1
whatis.cat1: "whatis - display manual page descriptions"
$ lexgrog broken.1
broken.1: parse failed
WHATIS PARSING
mandb (which uses the same code as lexgrog) parses the NAME section at
the top of each manual page looking for names and descriptions of the
features documented in each. While the parser is quite tolerant, as it
has to cope with a number of different forms that have historically been
used, it may sometimes fail to extract the required information.
When using the traditional man macro set, a correct NAME section looks
something like this:
.SH NAME
foo \- program to do something
Some manual pagers require the ‘\-’ to be exactly as shown; mandb is
more tolerant, but for compatibility with other systems it is neverthe-
less a good idea to retain the backslash.
On the left-hand side, there may be several names, separated by commas.
Names containing whitespace will be ignored to avoid pathological behav-
iour on certain ill-formed NAME sections. The text on the right-hand
side is free-form, and may be spread over multiple lines. If several
features with different descriptions are being documented in the same
manual page, the following form is therefore used:
.SH NAME
foo, bar \- programs to do something
.br
baz \- program to do nothing
(A macro which starts a new paragraph, like .PP, may be used instead of
the break macro .br.)
When using the BSD-derived mdoc macro set, a correct NAME section looks
something like this:
.Sh NAME
.Nm foo
.Nd program to do something
There are several common reasons why whatis parsing fails. Sometimes
authors of manual pages replace ‘.SH NAME’ with ‘.SH MYPROGRAM’, and
then mandb cannot find the section from which to extract the information
it needs. Sometimes authors include a NAME section, but place free-form
text there rather than ‘name \- description’. However, any syntax re-
sembling the above should be accepted.
SEE ALSO
apropos(1), man(1), whatis(1), mandb(8)
NOTES
lexgrog attempts to parse files containing .so requests, but will only
be able to do so correctly if the files are properly installed in a man-
ual page hierarchy.
AUTHOR
The code used by lexgrog to scan man pages was written by:
Wilf. (G.Wilford@ee.surrey.ac.uk).
Fabrizio Polacco (fpolacco@debian.org).
Colin Watson (cjwatson@debian.org).
Colin Watson wrote the current incarnation of the command-line front-
end, as well as this man page.
BUGS
https://gitlab.com/man-db/man-db/-/issues
https://savannah.nongnu.org/bugs/?group=man-db
2.13.1 2025-05-02 LEXGROG(1)
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