13. Invoking diff

The format for running the diff command is:

diff options... files...

In the simplest case, two file names from-file and to-file are given, and 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, 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, 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.

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

diff options begin with `-', so normally file names 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.

13.1 Options to diff

Summary of options to diff.

13.1 Options to diff

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.

`-a'

`--text'

Treat all files as text and compare them line-by-line, even if they do not seem to be text. See section 1.7 Binary Files and Forcing Text Comparisons.

`-b'

`--ignore-space-change'

Ignore changes in amount of white space. See section 1.2 Suppressing Differences in Blank and Tab Spacing.

`-B'

`--ignore-blank-lines'

Ignore changes that just insert or delete blank lines. See section 1.3 Suppressing Differences in Blank Lines.

`--binary'

Read and write data in binary mode. See section 1.7 Binary Files and Forcing Text Comparisons.

`-c'

Use the context output format, showing three lines of context. See section 2.3.1 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 2.3.1 Context Format. For proper operation, patch typically needs at least two lines of context.

On older systems, diff supports an obsolete option `-lines' that has effect when combined with `-c' or `-p'. POSIX 1003.1-2001 (see section 17. Standards conformance) does not allow this; use `-C lines' instead.

`--changed-group-format=format'

Use format to output a line group containing differing lines from both files in if-then-else format. See section 2.6.1 Line Group Formats.

`-d'

`--minimal'

Change the algorithm perhaps find a smaller set of changes. This makes diff slower (sometimes much slower). See section 6. diff Performance Tradeoffs.

`-D name'

`--ifdef=name'

Make merged `#ifdef' format output, conditional on the preprocessor macro name. See section 2.6 Merging Files with If-then-else.

`-e'

`--ed'

Make output that is a valid ed script. See section 2.5.1 ed Scripts.

`-E'

`--ignore-tab-expansion'

Ignore changes due to tab expansion. See section 1.2 Suppressing Differences in Blank and Tab Spacing.

`-f'

`--forward-ed'

Make output that looks vaguely like an ed script but has changes in the order they appear in the file. See section 2.5.2 Forward ed Scripts.

`-F regexp'

`--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 2.3.3.1 Showing Lines That Match Regular Expressions.

`--from-file=file'

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

`--help'

Output a summary of usage and then exit.

`--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 6. diff Performance Tradeoffs.

`-i'

`--ignore-case'

Ignore changes in case; consider upper- and lower-case letters equivalent. See section 1.4 Suppressing Case Differences.

`-I regexp'

`--ignore-matching-lines=regexp'

Ignore changes that just insert or delete lines that match regexp. See section 1.5 Suppressing Lines Matching a Regular Expression.

`--ignore-file-name-case'

Ignore case when comparing file names during recursive comparison. See section 4. Comparing Directories.

`-l'

`--paginate'

Pass the output through pr to paginate it. See section 5.2 Paginating diff Output.

`--label=label'

Use label instead of the file name in the context format (see section 2.3.1 Context Format) and unified format (see section 2.3.2 Unified Format) headers. See section 2.5.3 RCS Scripts.

`--left-column'

Print only the left column of two common lines in side by side format. See section 2.4.1 Controlling Side by Side Format.

`--line-format=format'

Use format to output all input lines in if-then-else format. See section 2.6.2 Line Formats.

`-n'

`--rcs'

Output RCS-format diffs; like `-f' except that each command specifies the number of lines affected. See section 2.5.3 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 4. 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 2.6.1 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 2.6.2 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 2.6.1 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 2.6.2 Line Formats.

`-p'

`--show-c-function'

Show which C function each change is in. See section 2.3.3.2 Showing C Function Headings.

`-q'

`--brief'

Report only whether the files differ, not the details of the differences. See section 1.6 Summarizing Which Files Differ.

`-r'

`--recursive'

When comparing directories, recursively compare any subdirectories found. See section 4. Comparing Directories.

`-s'

`--report-identical-files'

Report when two files are the same. See section 4. Comparing Directories.

`-S file'

`--starting-file=file'

When comparing directories, start with the file file. This is used for resuming an aborted comparison. See section 4. Comparing Directories.

`--speed-large-files'

Use heuristics to speed handling of large files that have numerous scattered small changes. See section 6. diff Performance Tradeoffs.

`--strip-trailing-cr'

Strip any trailing carriage return at the end of an input line. See section 1.7 Binary Files and Forcing Text Comparisons.

`--suppress-common-lines'

Do not print common lines in side by side format. See section 2.4.1 Controlling Side by Side Format.

`-t'

`--expand-tabs'

Expand tabs to spaces in the output, to preserve the alignment of tabs in the input files. See section 5.1 Preserving Tab Stop Alignment.

`-T'

`--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 5.1 Preserving Tab Stop Alignment.

`--to-file=file'

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

`-u'

Use the unified output format, showing three lines of context. See section 2.3.2 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 2.6.1 Line Group Formats.

`--unchanged-line-format=format'

Use format to output a line common to both files in if-then-else format. See section 2.6.2 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 4. 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 2.3.2 Unified Format. For proper operation, patch typically needs at least two lines of context.

On older systems, diff supports an obsolete option `-lines' that has effect when combined with `-u'. POSIX 1003.1-2001 (see section 17. Standards conformance) does not allow this; use `-U lines' instead.

`-v'

`--version'

Output version information and then exit.

`-w'

`--ignore-all-space'

Ignore white space when comparing lines. See section 1.2 Suppressing Differences in Blank and Tab Spacing.

`-W columns'

`--width=columns'

Output at most columns (default 130) print columns per line in side by side format. See section 2.4.1 Controlling Side by Side Format.

`-x pattern'

`--exclude=pattern'

When comparing directories, ignore files and subdirectories whose basenames match pattern. See section 4. Comparing Directories.

`-X file'

`--exclude-from=file'

When comparing directories, ignore files and subdirectories whose basenames match any pattern contained in file. See section 4. Comparing Directories.

`-y'

`--side-by-side'

Use the side by side output format. See section 2.4.1 Controlling Side by Side Format.