.\" Man page for lexgrog
.\"
.\" Copyright (c) 2001 Colin Watson <cjwatson@debian.org>
.\"
.\" You may distribute under the terms of the GNU General Public
.\" License as specified in the file COPYING that comes with the
.\" man-db distribution.
.pc
.TH LEXGROG 1 "%date%" "%version%" "Manual pager utils"
.SH NAME
lexgrog \- parse header information in man pages
.SH SYNOPSIS
.B lexgrog
.RB [\| \-m \||\| -c \|]
.RB [\| \-dfw?V \|]
.RB [\| \-E
.IR encoding \|]
.I file
\&.\|.\|.
.SH DESCRIPTION
.B lexgrog
is an implementation of the traditional \(lqgroff guess\(rq utility in
.BR lex .
It reads the list of files on its command line as either man page source
files or preformatted \(lqcat\(rq pages, and displays their name and
description as used by
.B apropos
and
.BR whatis ,
the list of preprocessing filters required by the man page before it is
passed to
.B nroff
or
.BR troff ,
or both.
.PP
If its input is badly formatted,
.B lexgrog
will print \(lqparse failed\(rq; this may be useful for external
programs that need to check man pages for correctness.
If one of
.BR lexgrog 's
input files is \(lq\-\(rq, it will read from standard input; if any input
file is compressed, a decompressed version will be read automatically.
.SH OPTIONS
.TP
.if !'po4a'hide' .BR \-d ", " \-\-debug
Print debugging information.
.TP
.if !'po4a'hide' .BR \-m ", " \-\-man
Parse input as man page source files.
This is the default if neither
.B \-\-man
nor
.B \-\-cat
is given.
.TP
.if !'po4a'hide' .BR \-c ", " \-\-cat
Parse input as preformatted man pages (\(lqcat pages\(rq).
.B \-\-man
and
.B \-\-cat
may not be given simultaneously.
.TP
.if !'po4a'hide' .BR \-w ", " \-\-whatis
Display the name and description from the man page's header, as used by
.B apropos
and
.BR whatis .
This is the default if neither
.B \-\-whatis
nor
.B \-\-filters
is given.
.TP
.if !'po4a'hide' .BR \-f ", " \-\-filters
Display the list of filters needed to preprocess the man page before
formatting with
.B nroff
or
.BR troff .
.TP
\fB\-E\fP \fIencoding\fP, \fB\-\-encoding\fP \fIencoding\fP
Override the guessed character set for the page to
.IR encoding .
.TP
.if !'po4a'hide' .BR \-? ", " \-\-help
Print a help message and exit.
.TP
.if !'po4a'hide' .B \-\-usage
Print a short usage message and exit.
.TP
.if !'po4a'hide' .BR \-V ", " \-\-version
Display version information.
.SH "EXIT STATUS"
.TP
.if !'po4a'hide' .B 0
Successful program execution.
.TP
.if !'po4a'hide' .B 1
Usage error.
.TP
.if !'po4a'hide' .B 2
.B lexgrog
failed to parse one or more of its input files.
.SH EXAMPLES
.nf
  $ 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
.fi
.SH WHATIS PARSING
.B %mandb%
(which uses the same code as
.BR lexgrog )
parses the
.B 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.
.PP
When using the traditional
.I man
macro set, a correct
.B NAME
section looks something like this:
.PP
.RS
.ft CW
.nf
\&.SH NAME
foo \e\- program to do something
.fi
.ft P
.RE
.PP
Some manual pagers require the \(oq\e\-\(cq to be exactly as shown;
.B %mandb%
is more tolerant, but for compatibility with other systems it is
nevertheless a good idea to retain the backslash.
.PP
On the left-hand side, there may be several names, separated by commas.
Names containing whitespace will be ignored to avoid pathological behaviour
on certain ill-formed
.B 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:
.PP
.RS
.ft CW
.nf
\&.SH NAME
foo, bar \e\- programs to do something
\&.br
baz \e\- program to do nothing
.fi
.ft P
.RE
.PP
(A macro which starts a new paragraph, like \f(CW.PP\fP, may be used instead
of the break macro \f(CW.br\fP.)
.PP
When using the BSD-derived
.I mdoc
macro set, a correct
.B NAME
section looks something like this:
.PP
.RS
.ft CW
.nf
\&.Sh NAME
\&.Nm foo
\&.Nd program to do something
.fi
.ft P
.RE

There are several common reasons why whatis parsing fails.
Sometimes authors of manual pages replace \(oq.SH NAME\(cq with
\(oq.SH MYPROGRAM\(cq, and then
.B %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 \(oqname \e\- description\(cq.
However, any syntax resembling the above should be accepted.
.SH "SEE ALSO"
.if !'po4a'hide' .IR apropos (1),
.if !'po4a'hide' .IR man (1),
.if !'po4a'hide' .IR whatis (1),
.if !'po4a'hide' .IR mandb (8)
.SH NOTES
.B 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 manual page
hierarchy.
.SH AUTHOR
The code used by
.B lexgrog
to scan man pages was written by:
.PP
.nf
.if !'po4a'hide' Wilf.\& (G.Wilford@ee.surrey.ac.uk).
.if !'po4a'hide' Fabrizio Polacco (fpolacco@debian.org).
.if !'po4a'hide' Colin Watson (cjwatson@debian.org).
.fi
.PP
Colin Watson wrote the current incarnation of the command-line
front-end, as well as this man page.
.SH BUGS
.if !'po4a'hide' https://gitlab.com/cjwatson/man-db/-/issues
.br
.if !'po4a'hide' https://savannah.nongnu.org/bugs/?group=man-db
