NAME
diff - find differences between two files
SYNOPSIS
diff [options] from-file to-file
DESCRIPTION
In the simplest case, diff compares the contents of the two
files from-file and to-file. A file name of - stands for
text read from the standard input. As a special case, diff
- - compares a copy of standard input to itself.
If from-file is a directory and to-file is not, diff com-
pares the file in from-file whose file name is that of to-
file, and vice versa. The non-directory file must not be -.
If both from-file and to-file are directories, diff compares
corresponding files in both directories, in alphabetical
order; this comparison is not recursive unless the -r or
--recursive option is given. diff never compares the actual
contents of a directory as if it were a file. The file that
is fully specified may not be standard input, because stan-
dard input is nameless and the notion of ``file with the
same name'' does not apply.
diff options begin with -, so normally from-file and to-file
may not begin with -. However, -- as an argument by itself
treats the remaining arguments as file names even if they
begin with -.
Options
Below is a summary of all of the options that GNU diff
accepts. Most options have two equivalent names, one of
which is a single letter preceded by -, and the other of
which is a long name preceded by --. Multiple single letter
options (unless they take an argument) can be combined into
a single command line word: -ac is equivalent to -a -c.
Long named options can be abbreviated to any unique prefix
of their name. Brackets ([ and ]) indicate that an option
takes an optional argument.
-lines
Show lines (an integer) lines of context. This option
does not specify an output format by itself; it has no
effect unless it is combined with -c or -u. This
option is obsolete. For proper operation, patch typi-
cally needs at least two lines of context.
-a Treat all files as text and compare them line-by-line,
even if they do not seem to be text.
-b Ignore changes in amount of white space.
-B Ignore changes that just insert or delete blank lines.
--brief
Report only whether the files differ, not the details
of the differences.
-c Use the context output format.
-C lines
--context[=lines]
Use the context output format, showing lines (an
integer) lines of context, or three if lines is not
given. For proper operation, patch typically needs at
least two lines of context.
--changed-group-format=format
Use format to output a line group containing differing
lines from both files in if-then-else format.
-d Change the algorithm to perhaps find a smaller set of
changes. This makes diff slower (sometimes much
slower).
-D name
Make merged if-then-else format output, conditional on
the preprocessor macro name.
-e
--ed Make output that is a valid ed script.
--exclude=pattern
When comparing directories, ignore files and subdirec-
tories whose basenames match pattern.
--exclude-from=file
When comparing directories, ignore files and subdirec-
tories whose basenames match any pattern contained in
file.
--expand-tabs
Expand tabs to spaces in the output, to preserve the
alignment of tabs in the input files.
-f Make output that looks vaguely like an ed script but
has changes in the order they appear in the file.
-F regexp
In context and unified format, for each hunk of differ-
ences, show some of the last preceding line that
matches regexp.
--forward-ed
Make output that looks vaguely like an ed script but
has changes in the order they appear in the file.
-h This option currently has no effect; it is present for
Unix compatibility.
-H Use heuristics to speed handling of large files that
have numerous scattered small changes.
--horizon-lines=lines
Do not discard the last lines lines of the common pre-
fix and the first lines lines of the common suffix.
-i Ignore changes in case; consider upper- and lower-case
letters equivalent.
-I regexp
Ignore changes that just insert or delete lines that
match regexp.
--ifdef=name
Make merged if-then-else format output, conditional on
the preprocessor macro name.
--ignore-all-space
Ignore white space when comparing lines.
--ignore-blank-lines
Ignore changes that just insert or delete blank lines.
--ignore-case
Ignore changes in case; consider upper- and lower-case
to be the same.
--ignore-matching-lines=regexp
Ignore changes that just insert or delete lines that
match regexp.
--ignore-space-change
Ignore changes in amount of white space.
--initial-tab
Output a tab rather than a space before the text of a
line in normal or context format. This causes the
alignment of tabs in the line to look normal.
-l Pass the output through pr to paginate it.
-L label
--label=label
Use label instead of the file name in the context for-
mat and unified format headers.
--left-column
Print only the left column of two common lines in side
by side format.
--line-format=format
Use format to output all input lines in in-then-else
format.
--minimal
Change the algorithm to perhaps find a smaller set of
changes. This makes diff slower (sometimes much
slower).
-n Output RCS-format diffs; like -f except that each com-
mand specifies the number of lines affected.
-N
--new-file
In directory comparison, if a file is found in only one
directory, treat it as present but empty in the other
directory.
--new-group-format=format
Use format to output a group of lines taken from just
the second file in if-then-else format.
--new-line-format=format
Use format to output a line taken from just the second
file in if-then-else format.
--old-group-format=format
Use format to output a group of lines taken from just
the first file in if-then-else format.
--old-line-format=format
Use format to output a line taken from just the first
file in if-then-else format.
-p Show which C function each change is in.
-P When comparing directories, if a file appears only in
the second directory of the two, treat it as present
but empty in the other.
--paginate
Pass the output through pr to paginate it.
-q Report only whether the files differ, not the details
of the differences.
-r When comparing directories, recursively compare any
subdirectories found.
--rcs
Output RCS-format diffs; like -f except that each com-
mand specifies the number of lines affected.
--recursive
When comparing directories, recursively compare any
subdirectories found.
--report-identical-files
-s Report when two files are the same.
-S file
When comparing directories, start with the file file.
This is used for resuming an aborted comparison.
--sdiff-merge-assist
Print extra information to help sdiff. sdiff uses this
option when it runs diff. This option is not intended
for users to use directly.
--show-c-function
Show which C function each change is in.
--show-function-line=regexp
In context and unified format, for each hunk of differ-
ences, show some of the last preceding line that
matches regexp.
--side-by-side
Use the side by side output format.
--speed-large-files
Use heuristics to speed handling of large files that
have numerous scattered small changes.
--starting-file=file
When comparing directories, start with the file file.
This is used for resuming an aborted comparison.
--suppress-common-lines
Do not print common lines in side by side format.
-t Expand tabs to spaces in the output, to preserve the
alignment of tabs in the input files.
-T Output a tab rather than a space before the text of a
line in normal or context format. This causes the
alignment of tabs in the line to look normal.
--text
Treat all files as text and compare them line-by-line,
even if they do not appear to be text.
-u Use the unified output format.
--unchanged-group-format=format
Use format to output a group of common lines taken from
both files in if-then-else format.
--unchanged-line-format=format
Use format to output a line common to both files in
if-then-else format.
--unidirectional-new-file
When comparing directories, if a file appears only in
the second directory of the two, treat it as present
but empty in the other.
-U lines
--unified[=lines]
Use the unified output format, showing lines (an
integer) lines of context, or three if lines is not
given. For proper operation, patch typically needs at
least two lines of context.
-v
--version
Output the version number of diff.
-w Ignore white space when comparing lines.
-W columns
--width=columns
Use an output width of columns in side by side format.
-x pattern
When comparing directories, ignore files and subdirec-
tories whose basenames match pattern.
-X file
When comparing directories, ignore files and subdirec-
tories whose basenames match any pattern contained in
file.
-y Use the side by side output format.
SEE ALSO
cmp(1), comm(1), diff3(1), ed(1), patch(1), pr(1), sdiff(1).
DIAGNOSTICS
An exit status of 0 means no differences were found, 1 means
some differences were found, and 2 means trouble.