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
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. 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-file may not begin with `-'. However, `--' as an
argument by itself treats the remaining arguments as file names even if
they begin with `-'.
An exit status of 0 means no differences were found, 1 means some
differences were found, and 2 means trouble.
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' (see section Context Format) or `-u'
(see section Unified Format). This option is obsolete. For proper
operation, patch typically needs at least two lines of context.
Use the context output format. See section Context Format.
`-C lines'
`--context[=lines]'
Use the context output format, showing lines (an integer) lines of
context, or three if lines is not given. See section Context Format.
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. See section Line Group Formats.
`-d'
Change the algorithm perhaps find a smaller set of changes. This makes
diff slower (sometimes much slower). See section diff Performance Tradeoffs.
`-D name'
Make merged `#ifdef' format output, conditional on the preprocessor
macro name. See section Merging Files with If-then-else.
`-e'
`--ed'
Make output that is a valid ed script. See section ed Scripts.
`--exclude=pattern'
When comparing directories, ignore files and subdirectories whose basenames
match pattern. See section Comparing Directories.
`--exclude-from=file'
When comparing directories, ignore files and subdirectories whose basenames
match any pattern contained in file. See section Comparing Directories.
`--expand-tabs'
Expand tabs to spaces in the output, to preserve the alignment of tabs
in the input files. See section Preserving Tabstop Alignment.
`-f'
Make output that looks vaguely like an ed script but has changes
in the order they appear in the file. See section Forward ed Scripts.
`-F regexp'
In context and unified format, for each hunk of differences, show some
of the last preceding line that matches regexp. See section Showing Lines That Match Regular Expressions.
`--forward-ed'
Make output that looks vaguely like an ed script but has changes
in the order they appear in the file. See section Forward ed Scripts.
`-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. See section diff Performance Tradeoffs.
`--horizon-lines=lines'
Do not discard the last lines lines of the common prefix
and the first lines lines of the common suffix.
See section diff Performance Tradeoffs.
`-i'
Ignore changes in case; consider upper- and lower-case letters
equivalent. See section Suppressing Case Differences.
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. See section Preserving Tabstop Alignment.
Use label instead of the file name in the context format
(see section Context Format) and unified format (see section Unified Format)
headers. See section RCS Scripts.
`--label=label'
Use label instead of the file name in the context format
(see section Context Format) and unified format (see section Unified Format)
headers.
Use format to output all input lines in if-then-else format.
See section Line Formats.
`--minimal'
Change the algorithm to perhaps find a smaller set of changes. This
makes diff slower (sometimes much slower). See section diff Performance Tradeoffs.
`-n'
Output RCS-format diffs; like `-f' except that each command
specifies the number of lines affected. See section RCS Scripts.
`-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. See section Comparing Directories.
`--new-group-format=format'
Use format to output a group of lines taken from just the second
file in if-then-else format. See section Line Group Formats.
`--new-line-format=format'
Use format to output a line taken from just the second file in
if-then-else format. See section Line Formats.
`--old-group-format=format'
Use format to output a group of lines taken from just the first
file in if-then-else format. See section Line Group Formats.
`--old-line-format=format'
Use format to output a line taken from just the first file in
if-then-else format. See section Line Formats.
When comparing directories, if a file appears only in the second
directory of the two, treat it as present but empty in the other.
See section Comparing Directories.
In context and unified format, for each hunk of differences, show some
of the last preceding line that matches regexp. See section Showing Lines That Match Regular Expressions.
Expand tabs to spaces in the output, to preserve the alignment of tabs
in the input files. See section Preserving Tabstop Alignment.
`-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. See section Preserving Tabstop Alignment.
Use the unified output format. See section Unified Format.
`--unchanged-group-format=format'
Use format to output a group of common lines taken from both files
in if-then-else format. See section Line Group Formats.
`--unchanged-line-format=format'
Use format to output a line common to both files in if-then-else
format. See section Line Formats.
`--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.
See section Comparing Directories.
`-U lines'
`--unified[=lines]'
Use the unified output format, showing lines (an integer) lines of
context, or three if lines is not given. See section Unified Format.
For proper operation, patch typically needs at least two lines of
context.