grog(1) General Commands Manual grog(1)
Name
grog - "groff guess"--infer the groff command a document requires
Synopsis
grog [groff-option ...] [--] [file ...]
grog -h
grog --help
grog -v
grog --version
Description
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.
Options
-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.
Details
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 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
infers 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
conceals 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
Exit status
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.
Examples
Running
grog /opt/local/share/doc/groff-1.24.1/meintro.me
at the command line results in
groff -me /opt/local/share/doc/groff-1.24.1/meintro.me
because grog recognizes that the file meintro.me is written using
macros from the me package. The command
grog /opt/local/share/doc/groff-1.24.1/pic.ms
outputs
groff -e -p -t -ms /opt/local/share/doc/groff-1.24.1/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 /opt/
local/share/doc/groff-1.24.1 if you'd like to try this example
yourself.)
Authors
grog was originally written in Bourne shell by James Clark. The
current implementation in Perl was written by Bernd Warken <groff-bernd
.warken-72@web.de> and heavily revised by G. Branden Robinson
<g.branden.robinson@gmail.com>.
See also
groff(1)
groff 1.24.1 2026-05-15 grog(1)
groff 1.24.1 - Generated Mon May 18 09:31:06 CDT 2026