gdiffmk(1) General Commands Manual gdiffmk(1)
Name
gdiffmk - mark differences between groff/nroff/troff files
Synopsis
gdiffmk [-a add-mark] [-c change-mark] [-d delete-mark]
[-x diff-command] [-D [-B] [-M mark1 mark2]] [--] file1 file2
[output-file]
gdiffmk --help
gdiffmk --version
Description
gdiffmk compares two roff(7) documents, file1 and file2, and writes
another, derived from both, to the standard output stream (or
output-file), adding margin character (mc) requests at places in the
output where the input documents differ. gdiffmk does not interpret
the source documents; it treats roff comments and nilpotent changes to
formatting as meaningful. For example, it does not know that \h'3m',
\h'(1 * 3m)', and \h'3m+0' all mean the same thing. If the file1 or
file2 argument is "-", gdiffmk reads the standard input stream for that
input. If the output operand is present, gdiffmk writes output to a
file of that name. If it is "-" or absent, gdiffmk writes output to
the standard output stream. "-" cannot be both an input and output
operand.
Options
--help displays a usage message and --version shows version
information; both exit afterward.
-a add-mark
Annotate material absent from file1 but present in file2 with
add-mark (default: "+").
-B Suppress br requests normally inserted by -D option. Use with
caution; such requests are the only way to guarantee that
deletions and small changes are marked.
-c change-mark
Annotate material differing between file1 and file2 with
change-mark (default: "|").
-d delete-mark
Annotate material present in file1 but absent from file2 with
delete-mark (default: "*").
-D Mark changed and deleted material with surrounding delimiters.
-M mark1 mark2
Use mark1 (default: "[[") and mark2 (default: "]]") as
delimiters when using the -D option.
-x diff-command
Use the diff-command program to perform the comparison of file1
and file2. diff-command (default: diff) must accept GNU
diff(1)'s -D extension option.
-- Treat all subsequent arguments as file names, even if they begin
with "-".
Exit status
gdiffmk exits with status 0 if the input files are the same; 1 if they
differ; 2 upon a usage error; 3 if the system's diff(1) or sh(1)
commands do not support features gdiffmk requires; and 4 if the output
argument is a duplicate of file1 or file2.
Caveats
The output is not necessarily compatible with all macro packages or
preprocessors. A reliable workaround is to run gdiffmk on the output
of the final preprocessor instead of the input source.
gdiffmk relies on the -D option of GNU diff to make a merged "#ifdef"
output format. Busybox diff is known to not support it. Also see the
-x diff-command option.
Authors
gdiffmk was written by Mike Bianchi <MBianchi@Foveal.com>, now retired.
It is maintained by the groff developers.
See also
groff(1), nroff(1), troff(1), roff(7), diff(1)
groff 1.24.1 2026-05-15 gdiffmk(1)
groff 1.24.1 - Generated Mon May 18 07:56:11 CDT 2026