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 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.

       --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  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.

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 manual 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