Invoking @command{diff}

The format for running the @command{diff} command is:

diff options... files...

In the simplest case, two file names from-file and to-file are given, and @command{diff} compares the contents of 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 one file is a directory and the other is not, @command{diff} compares the file in the directory whose name is that of the non-directory. The non-directory file must not be `-'.

If two file names are given and both are directories, @command{diff} compares corresponding files in both directories, in alphabetical order; this comparison is not recursive unless the @option{-r} or @option{--recursive} option is given. @command{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.

If the @option{--from-file=file} option is given, the number of file names is arbitrary, and file is compared to each named file. Similarly, if the @option{--to-file=file} option is given, each named file is compared to file.

@command{diff} options begin with `-', so normally file names may not begin with `-'. However, @option{--} 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.

Options to @command{diff}

Below is a summary of all of the options that GNU @command{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: @option{-ac} is equivalent to @option{-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.

@option{-a}

@option{--text}

Treat all files as text and compare them line-by-line, even if they do not seem to be text. See section Binary Files and Forcing Text Comparisons.

@option{-b}

@option{--ignore-space-change}

Ignore changes in amount of white space. See section Suppressing Differences in Blank and Tab Spacing.

@option{-B}

@option{--ignore-blank-lines}

Ignore changes that just insert or delete blank lines. See section Suppressing Differences in Blank Lines.

@option{--binary}

Read and write data in binary mode. See section Binary Files and Forcing Text Comparisons.

@option{-c}

Use the context output format, showing three lines of context. See section Context Format.

@option{-C lines}

@option{--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, @command{patch} typically needs at least two lines of context. On older systems, @command{diff} supports an obsolete option @option{-lines} that has effect when combined with @option{-c} or @option{-p}. POSIX 1003.1-2001 (see section Standards conformance) does not allow this; use @option{-C lines} instead.

@option{--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.

@option{-d}

@option{--minimal}

Change the algorithm perhaps find a smaller set of changes. This makes @command{diff} slower (sometimes much slower). See section @command{diff} Performance Tradeoffs.

@option{-D name}

@option{--ifdef=name}

Make merged `#ifdef' format output, conditional on the preprocessor macro name. See section Merging Files with If-then-else.

@option{-e}

@option{--ed}

Make output that is a valid @command{ed} script. See section @command{ed} Scripts.

@option{-E}

@option{--ignore-tab-expansion}

Ignore changes due to tab expansion. See section Suppressing Differences in Blank and Tab Spacing.

@option{-f}

@option{--forward-ed}

Make output that looks vaguely like an @command{ed} script but has changes in the order they appear in the file. See section Forward @command{ed} Scripts.

@option{-F regexp}

@option{--show-function-line=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.

@option{--from-file=file}

Compare file to each operand; file may be a directory.

@option{--help}

Output a summary of usage and then exit.

@option{--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 @command{diff} Performance Tradeoffs.

@option{-i}

@option{--ignore-case}

Ignore changes in case; consider upper- and lower-case letters equivalent. See section Suppressing Case Differences.

@option{-I regexp}

@option{--ignore-matching-lines=regexp}

Ignore changes that just insert or delete lines that match regexp. See section Suppressing Lines Matching a Regular Expression.

@option{--ignore-file-name-case}

Ignore case when comparing file names during recursive comparison. See section Comparing Directories.

@option{-l}

@option{--paginate}

Pass the output through @command{pr} to paginate it. See section Paginating @command{diff} Output.

@option{--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. See section RCS Scripts.

@option{--left-column}

Print only the left column of two common lines in side by side format. See section Controlling Side by Side Format.

@option{--line-format=format}

Use format to output all input lines in if-then-else format. See section Line Formats.

@option{-n}

@option{--rcs}

Output RCS-format diffs; like @option{-f} except that each command specifies the number of lines affected. See section RCS Scripts.

@option{-N}

@option{--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.

@option{--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.

@option{--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.

@option{--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.

@option{--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.

@option{-p}

@option{--show-c-function}

Show which C function each change is in. See section Showing C Function Headings.

@option{-q}

@option{--brief}

Report only whether the files differ, not the details of the differences. See section Summarizing Which Files Differ.

@option{-r}

@option{--recursive}

When comparing directories, recursively compare any subdirectories found. See section Comparing Directories.

@option{-s}

@option{--report-identical-files}

Report when two files are the same. See section Comparing Directories.

@option{-S file}

@option{--starting-file=file}

When comparing directories, start with the file file. This is used for resuming an aborted comparison. See section Comparing Directories.

@option{--speed-large-files}

Use heuristics to speed handling of large files that have numerous scattered small changes. See section @command{diff} Performance Tradeoffs.

@option{--strip-trailing-cr}

Strip any trailing carriage return at the end of an input line. See section Binary Files and Forcing Text Comparisons.

@option{--suppress-common-lines}

Do not print common lines in side by side format. See section Controlling Side by Side Format.

@option{-t}

@option{--expand-tabs}

Expand tabs to spaces in the output, to preserve the alignment of tabs in the input files. See section Preserving Tab Stop Alignment.

@option{-T}

@option{--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. See section Preserving Tab Stop Alignment.

@option{--to-file=file}

Compare each operand to file; file may be a directory.

@option{-u}

Use the unified output format, showing three lines of context. See section Unified Format.

@option{--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.

@option{--unchanged-line-format=format}

Use format to output a line common to both files in if-then-else format. See section Line Formats.

@option{--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.

@option{-U lines}

@option{--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, @command{patch} typically needs at least two lines of context. On older systems, @command{diff} supports an obsolete option @option{-lines} that has effect when combined with @option{-u}. POSIX 1003.1-2001 (see section Standards conformance) does not allow this; use @option{-U lines} instead.

@option{-v}

@option{--version}

Output version information and then exit.

@option{-w}

@option{--ignore-all-space}

Ignore white space when comparing lines. See section Suppressing Differences in Blank and Tab Spacing.

@option{-W columns}

@option{--width=columns}

Output at most columns (default 130) print columns per line in side by side format. See section Controlling Side by Side Format.

@option{-x pattern}

@option{--exclude=pattern}

When comparing directories, ignore files and subdirectories whose basenames match pattern. See section Comparing Directories.

@option{-X file}

@option{--exclude-from=file}

When comparing directories, ignore files and subdirectories whose basenames match any pattern contained in file. See section Comparing Directories.

@option{-y}

@option{--side-by-side}

Use the side by side output format. See section Controlling Side by Side Format.

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