lexgrog — parse header information in man pages


lexgrog [-m|-c] [-dfw?V] [-E encoding] file ...


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.


-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 before 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.


Print a short usage message and exit.

-V, --version

Display version information.

Exit Status


Successful program execution.


Usage error.


lexgrog failed to parse one or more of its input files.


  $ lexgrog man.1
  man.1: "man - an interface to the on-line reference manuals"
  $ lexgrog -fw man.1
  man.1 (t): "man - an interface to the on-line 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:

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 nevertheless 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 behaviour 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:

foo, bar \- programs to do something
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:

.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 resembling the above should be accepted.

See Also

apropos(1), man(1), whatis(1), mandb(8)


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.


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.

Referenced By

man(7), mandb(8).

2019-08-26 2.8.7 Manual pager utils