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Name | Synopsis | Description | Options | Details | Exit status | Examples | Authors | See also | COLOPHON |
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grog(1) General Commands Manual grog(1)
grog - “groff guess”—infer the groff command a document requires
grog [groff-option ...] [--] [file ...]
grog -h
grog --help
grog -v
grog --version
grog reads its input and guesses which groff(1) options are needed
to render it. If no operands are given, or if file is “-”, grog
reads the standard input stream. The corresponding groff command
is normally written to the standard output stream.
-h and --help display a usage message, whereas -v and --version
display version information; all exit afterward.
All other specified short options (that is, arguments beginning
with a minus sign “-” followed by a letter) are interpreted as
groff options or option clusters with or without an option
argument. Such options are included in the constructed groff
command line.
grog reads each file operand, pattern-matching strings that are
statistically likely to be characteristic of roff(7) documents.
It tries to guess which of the following groff options are
required to correctly render the input: -e, -g, -G, -j, -p, -R, -t
(preprocessors); and -man, -mdoc, -mdoc-old, -me, -mm, -mom, and
-ms (macro packages). The inferred groff command including these
options and any file parameters is written to the standard output
stream.
It is possible to specify arbitrary groff options on the command
line. These are included in the inferred command without change.
Choices of groff options include -C to enable AT&T troff
compatibility mode and -T to select a non-default output device.
If the input is not encoded in ISO 646:1991 IRV (US-ASCII) or
ISO Latin-1 (8859-1), we advise specifying a groff option to run
the preconv(1;) see the -D, -k, and -K options of groff(1). For
UTF-8 input, -k is a good choice.
groff may issue diagnostic messages when an inappropriate -m
option, or multiple conflicting ones, are specified.
Consequently, it is best to specify no -m options to grog unless
it cannot correctly infer all of the -m arguments a document
requires. A roff document can also be written without recourse to
any macro package. In such cases, grog will infer a groff command
without an -m option.
Limitations
grog presumes that the input does not change the escape, control,
or no-break control characters. grog does not parse roff input
line continuation or control structures (brace escape sequences
and the “if”, “ie”, and “el” requests) nor groff's “while”. Thus
the input
.if \
t .NH 1
.if n .SH
Introduction
will conceal the use of the ms macros NH and SH from grog. Such
constructions are regarded by grog's implementors as
insufficiently common to cause many inference problems.
Preprocessors can be even stricter when matching macro calls that
bracket the regions of an input file they replace. pic, for
example, requires PS, PE, and PF calls to immediately follow the
default control character at the beginning of a line.
Detection of the -s option (the soelim(1) preprocessor) is tricky;
to correctly infer its necessity would require grog to recursively
open all files given as arguments to the .so request under the
same conditions that soelim itself does so; see its man page.
Recall that soelim is necessary only if sourced files need to be
preprocessed. Therefore, as a workaround, you may want to run the
input through soelim manually, piping it to grog, and compare the
output to running grog on the input directly. If the “soelim”ed
input causes grog to infer additional preprocessor options, then
-s is likely necessary.
$ printf ".TS\nl.\nI'm a table.\n.TE\n" > 3.roff
$ printf ".so 3.roff\n" > 2.roff
$ printf ".XP\n.so 2.roff\n" > 1.roff
$ grog 1.roff
groff -ms 1.roff
$ soelim 1.roff | grog
groff -t -ms -
In the foregoing example, we see that this procedure enabled grog
to detect tbl(1) macros, so we would add -s as well as the
detected -t option to a revised grog or groff command.
$ grog -st 1.roff
groff -st -ms 1.roff
grog exits with status 1 if a macro package appears to be in use
by the input document, but grog was unable to infer which one, or
2 if there were problems handling an option or operand. It
otherwise exits with status 0. Inferring no preprocessors or
macro packages is not an error condition; a valid roff document
need not use either. Even plain text is valid input, if one is
mindful of the syntax of the control and escape characters.
Running
grog /usr/local/share/doc/groff-1.23.0/meintro.me
at the command line results in
groff -me /usr/local/share/doc/groff-1.23.0/meintro.me
because grog recognizes that the file meintro.me is written using
macros from the me package. The command
grog /usr/local/share/doc/groff-1.23.0/pic.ms
outputs
groff -e -p -t -ms /usr/local/share/doc/groff-1.23.0/pic.ms
on the other hand. Besides discerning the ms macro package, grog
recognizes that the file pic.ms additionally needs the combination
of -t for tbl, -e for eqn, and -p for pic.
Consider a file doc/grnexampl.me, which uses the grn preprocessor
to include a gremlin(1) picture file in an me document. Let's say
we want to suppress color output, produce a DVI file, and get
backtraces for any errors that troff encounters. The command
grog -bc -Idoc -Tdvi doc/grnexmpl.me
is processed by grog into
groff -bc -Idoc -Tdvi -e -g -me doc/grnexmpl.me
where we can see that grog has inferred the me macro package along
with the eqn and grn preprocessors. (The input file is located in
/usr/local/share/doc/groff-1.23.0 if you'd like to try this
example yourself.)
grog was originally written in Bourne shell by James Clark. The
current implementation in Perl was written by Bernd Warken
⟨[email protected]⟩ and heavily revised by G. Branden
Robinson ⟨[email protected]⟩.
groff(1)
This page is part of the groff (GNU troff) project. Information
about the project can be found at
⟨http://www.gnu.org/software/groff/⟩. If you have a bug report for
this manual page, see ⟨http://www.gnu.org/software/groff/⟩. This
page was obtained from the project's upstream Git repository
⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2025-08-11. (At
that time, the date of the most recent commit that was found in
the repository was 2025-08-09.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
groff 1.23.0.2722-658f-dirty 2025-01-02 grog(1)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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