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Comparing and Merging Files with GNU diff and patch
by David MacKenzie, Paul Eggert, and Richard Stallman
Paperback (6"x9"), 120 pages
ISBN 0954161750
RRP £12.95 ($19.95)

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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.
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