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.
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 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:
.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 resembling the above should be accepted.
apropos(1), man(1), whatis(1), mandb(8)
The code used by lexgrog to scan man pages was written by:
Wilf. (G.Wilford@ee.surrey.ac.uk). Fabrizio Polacco (email@example.com). Colin Watson (firstname.lastname@example.org).
Colin Watson wrote the current incarnation of the command-line front-end, as well as this man page.