Display the differences between two files, or each corresponding file in two directories.
Each set of differences is called a "diff" or "patch". For files that are identical, 'diff' normally produces no output; for binary (non-text) files, `diff' normally reports only that they are different.
Syntax
diff [options] from-file to-file
Options
Multiple single letter options (unless they take an argument) can be combined into a single command-line word: so `-ac' is equivalent to `-a -c'.
-lines Show lines lines of context. This option is obsolete.
-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 dif-
fering lines from both files in if-then-else for-
mat.
-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 subdi-
rectories whose basenames match pattern.
--exclude-from=file
When comparing directories, ignore files and subdi-
rectories whose basenames match any pattern con-
tained 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
differences, 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
prefix and the first lines lines of the common suf-
fix.
-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
format 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
command 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
command 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 compar-
ison.
--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
differences, 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 compar-
ison.
--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 for-
mat.
-x pattern
When comparing directories, ignore files and subdi-
rectories whose basenames match pattern.
-X file
When comparing directories, ignore files and subdi-
rectories whose basenames match any pattern con-
tained in file.
-y Use the side by side output format.
Notes
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.
If from-file is a directory and to-file is not, diff compares 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.
As a special case, diff - - compares a copy of standard input to itself.
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 standard 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-filemay not begin with -. However, -- as an argument by itself treats the remaining arguments as file names even if they begin with -.
“In order to really enjoy a dog, one doesn't merely try to train him to be semihuman. The point of it is to open oneself to the possibility of becoming partly a dog” - Edward Hoagland
Related:
diff man page - Apple.com
patch - apply a diff file to an original
comm - Compare two sorted files line by line
ed - Line editor
cmp - Compare two files
diff3 - Show differences among three files
FileMerge - GUI tool to compare two ASCII files/folders (Developer tools)
pr - Convert text files for printing
sdiff - Merge two files interactively
