DIFF(1)                     General Commands Manual                    DIFF(1)

NAME
     diff – differential file and directory comparator

SYNOPSIS
     diff [-aBbdipTtw] [-c | -e | -f | -n | -q | -u | -y]
          [-A algo | --algorithm algo] [--brief] [--color=when]
          [--changed-group-format GFMT] [--ed] [--expand-tabs] [--forward-ed]
          [--ignore-all-space] [--ignore-case] [--ignore-space-change]
          [--initial-tab] [--minimal] [--no-ignore-file-name-case] [--normal]
          [--rcs] [--show-c-function] [--starting-file] [--speed-large-files]
          [--strip-trailing-cr] [--tabsize number] [--text] [--unified]
          [-I pattern | --ignore-matching-lines pattern]
          [-F pattern | --show-function-line pattern]
          [-L label | --label label] file1 file2
     diff [-aBbdilpTtw] [-A algo | --algorithm algo]
          [-I pattern | --ignore-matching-lines pattern]
          [-F pattern | --show-function-line pattern]
          [-L label | --label label] [--brief] [--color=when]
          [--changed-group-format GFMT] [--ed] [--expand-tabs] [--forward-ed]
          [--ignore-all-space] [--ignore-case] [--ignore-space-change]
          [--initial-tab] [--minimal] [--no-ignore-file-name-case] [--normal]
          [--paginate] [--rcs] [--show-c-function] [--speed-large-files]
          [--starting-file] [--strip-trailing-cr] [--tabsize number] [--text]
          -C number | -context number file1 file2
     diff [-aBbdiltw] [-A algo | --algorithm algo]
          [-I pattern | --ignore-matching-lines pattern] [--brief]
          [--color=when] [--changed-group-format GFMT] [--ed] [--expand-tabs]
          [--forward-ed] [--ignore-all-space] [--ignore-case]
          [--ignore-space-change] [--initial-tab] [--minimal]
          [--no-ignore-file-name-case] [--normal] [--paginate] [--rcs]
          [--show-c-function] [--speed-large-files] [--starting-file]
          [--strip-trailing-cr] [--tabsize number] [--text]
          -D string | --ifdef string file1 file2
     diff [-aBbdilpTtw] [-A algo | --algorithm algo]
          [-I pattern | --ignore-matching-lines pattern]
          [-F pattern | --show-function-line pattern]
          [-L label | --label label] [--brief] [--color=when]
          [--changed-group-format GFMT] [--ed] [--expand-tabs] [--forward-ed]
          [--ignore-all-space] [--ignore-case] [--ignore-space-change]
          [--initial-tab] [--minimal] [--no-ignore-file-name-case] [--normal]
          [--paginate] [--rcs] [--show-c-function] [--speed-large-files]
          [--starting-file] [--strip-trailing-cr] [--tabsize number] [--text]
          -U number | --unified number file1 file2
     diff [-aBbdilNPprsTtw] [-c | -e | -f | -n | -q | -u]
          [-A algo | --algorithm algo] [--brief] [--color=when]
          [--changed-group-format GFMT] [--context] [--ed] [--expand-tabs]
          [--forward-ed] [--ignore-all-space] [--ignore-case]
          [--ignore-space-change] [--initial-tab] [--minimal] [--new-file]
          [--no-ignore-file-name-case] [--normal] [--paginate] [--rcs]
          [--recursive] [--report-identical-files] [--show-c-function]
          [--speed-large-files] [--strip-trailing-cr] [--tabsize number]
          [--text] [--unidirectional-new-file] [--unified]
          [-I pattern | --ignore-matching-lines pattern]
          [-F pattern | --show-function-line pattern]
          [-L label | --label label] [-S name | --starting-file name]
          [-X file | --exclude-from file] [-x pattern | --exclude pattern]
          dir1 dir2
     diff [-aBbditwW] [--color=when] [--expand-tabs] [--ignore-all-blanks]
          [--ignore-blank-lines] [--ignore-case] [--minimal]
          [--no-ignore-file-name-case] [--strip-trailing-cr]
          [--suppress-common-lines] [--tabsize number] [--text] [--width]
          -y | --side-by-side file1 file2
     diff [--help] [--version]

DESCRIPTION
     The diff utility compares the contents of file1 and file2 and writes to
     the standard output the list of changes necessary to convert one file
     into the other.  No output is produced if the files are identical.

     Output options (mutually exclusive):

     -C number --context number
             Like -c but produces a diff with number lines of context.

     -c      Produces a diff with 3 lines of context.  With -c the output
             format is modified slightly: the output begins with
             identification of the files involved and their creation dates and
             then each change is separated by a line with fifteen *'s.  The
             lines removed from file1 are marked with ‘- ’; those added to
             file2 are marked ‘+ ’.  Lines which are changed from one file to
             the other are marked in both files with ‘! ’.  Changes which lie
             within 3 lines of each other are grouped together on output.

     -D string --ifdef string
             Creates a merged version of file1 and file2 on the standard
             output, with C preprocessor controls included so that a
             compilation of the result without defining string is equivalent
             to compiling file1, while defining string will yield file2.

     -e --ed
             Produces output in a form suitable as input for the editor
             utility, ed(1), which can then be used to convert file1 into
             file2.

             Note that when comparing directories with -e, the resulting file
             may no longer be interpreted as an ed(1) script.  Output is added
             to indicate which file each set of ed(1) commands applies to.
             These hunks can be manually extracted to produce an ed(1) script,
             which can also be applied with patch(1).

     -f --forward-ed
             Identical output to that of the -e flag, but in reverse order.
             It cannot be digested by ed(1).

     --help  This option prints a summary to stdout and exits with status 0.

     -n      Produces a script similar to that of -e, but in the opposite
             order and with a count of changed lines on each insert or delete
             command.  This is the form used by rcsdiff.

     -q --brief
             Just print a line when the files differ.  Does not output a list
             of changes.

     -U number --unified number
             Like -u but produces a diff with number lines of context.

     -u      Produces a unified diff with 3 lines of context.  A unified diff
             is similar to the context diff produced by the -c option.
             However, unlike with -c, all lines to be changed (added and/or
             removed) are present in a single section.

     --version
             This option prints a version string to stdout and exits with
             status 0.

     -y --side-by-side
             Output in two columns with a marker between them.  The marker can
             be one of the following:

                   space   Corresponding lines are identical.
                   '|'     Corresponding lines are different.
                   '<'     Files differ and only the first file contains the
                           line.
                   '>'     Files differ and only the second file contains the
                           line.

     Comparison options:

     -A algo, --algorithm algo
             Configure the algorithm used when comparing files.  diff supports
             3 algorithms:

             myers   Myers diff algorithm performs a O(ND) comparison between
                     the two files.  An optimisation is present when worst
                     case files are detected it causes the Myers algorithm to
                     bails out and produces correct, but non-optimal diff
                     output.
             patience
                     The Patience variant of the Myers algorithm, this variant
                     attempts to create more aesthetically pleasing diff
                     output by logically grouping lines.
             stone   The Stone algorithm looks for the longest common
                     subsequence between compared files.  Stone encounters
                     worst case performance when there are long common
                     subsequences.  In large files this can lead to a
                     significant performance impact.  The Stone algorithm is
                     maintained for compatibility.

             The default diff algorithm when this flag is not given is
             “myers”.  diff will fallback to the “stone” algorithm if the
             “myers” algorithm cannot be supported with the given options and
             the algorithm has not been set explicitly.

             The default algorithm is affected by the POSIXLY_CORRECT and
             POSIX_PEDANTIC environment variables.  When either variable is
             set the default algorithm will be “stone”.

             If the diff algorithm is selected, but cannot be supported with
             the given options diff will produce an error.

     -a --text
             Treat all files as ASCII text.  Normally diff will simply print
             “Binary files ... differ” if files contain binary characters.
             Use of this option forces diff to produce a diff.

     -B --ignore-blank-lines
             Causes chunks that include only blank lines to be ignored.

     -b --ignore-space-change
             Causes trailing blanks (spaces and tabs) to be ignored, and other
             strings of blanks to compare equal.

     --color=[when]
             Color the additions green, and removals red, or the value in the
             DIFFCOLORS environment variable.  The possible values of when are
             “never”, “always” and “auto”.  auto will use color if the output
             is a tty and the COLORTERM environment variable is set to a non-
             empty string.

     -d --minimal
             Try very hard to produce a diff as small as possible.  This may
             consume a lot of processing power and memory when processing
             large files with many changes.

     -F pattern, --show-function-line pattern
             Like -p, but display the last line that matches provided pattern.

     -I pattern --ignore-matching-lines pattern
             Ignores changes, insertions, and deletions whose lines match the
             extended regular expression pattern.  Multiple -I patterns may be
             specified.  All lines in the change must match some pattern for
             the change to be ignored.  See re_format(7) for more information
             on regular expression patterns.

     -i --ignore-case
             Ignores the case of letters.  E.g., “A” will compare equal to
             “a”.

     -l --paginate
             Pass the output through pr(1) to paginate it.

     -L label --label label
             Print label instead of the first (and second, if this option is
             specified twice) file name and time in the context or unified
             diff header.

     -p --show-c-function
             With unified and context diffs, show with each change the first
             40 characters of the last line before the context beginning with
             a letter, an underscore or a dollar sign.  For C and Objective-C
             source code following standard layout conventions, this will show
             the prototype of the function the change applies to.

     -T --initial-tab
             Print a tab rather than a space before the rest of the line for
             the normal, context or unified output formats.  This makes the
             alignment of tabs in the line consistent.

     -t --expand-tabs
             Will expand tabs in output lines.  Normal or -c output adds
             character(s) to the front of each line which may screw up the
             indentation of the original source lines and make the output
             listing difficult to interpret.  This option will preserve the
             original source's indentation.

     -w --ignore-all-blanks
             Is similar to -b --ignore-space-change but causes whitespace
             (blanks and tabs) to be totally ignored.  E.g., “if ( a == b )”
             will compare equal to “if(a==b)”.

     -W number --width number
             Output at most number columns when using side by side format.
             The default value is 130.  Note that unless

     -t      was specified, diff will always align the second column to a tab
             stop, so values of --width smaller than approximately five times
             the value of --tabsize may yield surprising results.

     --changed-group-format GFMT
             Format input groups in the provided

             the format is a string with special keywords:

             %<  lines from FILE1

             %<  lines from FILE2

     --ignore-file-name-case
             ignore case when comparing file names

     --no-ignore-file-name-case
             do not ignore case when comparing file names (default)

     --normal
             default diff output

     --speed-large-files
             stub option for compatibility with GNU diff

     --strip-trailing-cr
             strip carriage return on input files

     --suppress-common-lines
             Do not output common lines when using the side by side format

     --tabsize number
             Number of spaces representing a tab (default 8)

     Directory comparison options:

     -N --new-file
             If a file is found in only one directory, act as if it was found
             in the other directory too but was of zero size.

     -P --unidirectional-new-file
             If a file is found only in dir2, act as if it was found in dir1
             too but was of zero size.

     -r --recursive
             Causes application of diff recursively to common subdirectories
             encountered.

     -S name --starting-file name
             Re-starts a directory diff in the middle, beginning with file
             name.

     -s --report-identical-files
             Causes diff to report files which are the same, which are
             otherwise not mentioned.

     -X file --exclude-from file
             Exclude files and subdirectories from comparison whose basenames
             match lines in file.  Multiple -X options may be specified.

     -x pattern --exclude pattern
             Exclude files and subdirectories from comparison whose basenames
             match pattern.  Patterns are matched using shell-style globbing
             via fnmatch(3).  Multiple -x options may be specified.

     If both arguments are directories, diff sorts the contents of the
     directories by name, and then runs the regular file diff algorithm,
     producing a change list, on text files which are different.  Binary files
     which differ, common subdirectories, and files which appear in only one
     directory are described as such.  In directory mode only regular files
     and directories are compared.  If a non-regular file such as a device
     special file or FIFO is encountered, a diagnostic message is printed.

     If only one of file1 and file2 is a directory, diff is applied to the
     non-directory file and the file contained in the directory file with a
     filename that is the same as the last component of the non-directory
     file.

     If either file1 or file2 is ‘-’, the standard input is used in its place.

   Output Style
     The default (without -e, -c, or -n --rcs options) output contains lines
     of these forms, where XX, YY, ZZ, QQ are line numbers respective of file
     order.

     XXaYY        At (the end of) line XX of file1, append the contents of
                  line YY of file2 to make them equal.
     XXaYY,ZZ     Same as above, but append the range of lines, YY through ZZ
                  of file2 to line XX of file1.
     XXdYY        At line XX delete the line.  The value YY tells to which
                  line the change would bring file1 in line with file2.
     XX,YYdZZ     Delete the range of lines XX through YY in file1.
     XXcYY        Change the line XX in file1 to the line YY in file2.
     XX,YYcZZ     Replace the range of specified lines with the line ZZ.
     XX,YYcZZ,QQ  Replace the range XX,YY from file1 with the range ZZ,QQ from
                  file2.

     These lines resemble ed(1) subcommands to convert file1 into file2.  The
     line numbers before the action letters pertain to file1; those after
     pertain to file2.  Thus, by exchanging a for d and reading the line in
     reverse order, one can also determine how to convert file2 into file1.
     As in ed(1), identical pairs (where num1 = num2) are abbreviated as a
     single number.

ENVIRONMENT
     DIFFCOLORS  The value of this variable is the form add:rm, where add is
                 the ASCII escape sequence for additions and rm is the ASCII
                 escape sequence for deletions.  If this is unset, diff uses
                 green for additions and red for removals.

FILES
     /tmp/diff.XXXXXXXX  Temporary file used when comparing a device or the
                         standard input.  Note that the temporary file is
                         unlinked as soon as it is created so it will not show
                         up in a directory listing.

EXIT STATUS
     The diff utility exits with one of the following values:

           0       No differences were found.
           1       Differences were found.
           >1      An error occurred.

     The --help and --version options exit with a status of 0.

EXAMPLES
     Compare old_dir and new_dir recursively generating an unified diff and
     treating files found only in one of those directories as new files:

           $ diff -ruN /path/to/old_dir /path/to/new_dir

     Same as above but excluding files matching the expressions “*.h” and
     “*.c”:

           $ diff -ruN -x '*.h' -x '*.c' /path/to/old_dir /path/to/new_dir

     Show a single line indicating if the files differ:

           $ diff -q /boot/loader.conf /boot/defaults/loader.conf
           Files /boot/loader.conf and /boot/defaults/loader.conf differ

     Assuming a file named example.txt with the following contents:

           FreeBSD is an operating system
           Linux is a kernel
           OpenBSD is an operating system

     Compare stdin with example.txt excluding from the comparison those lines
     containing either "Linux" or "Open":

           $ echo "FreeBSD is an operating system" | diff -q -I 'Linux|Open' example.txt -

LEGACY DESCRIPTION
     The unified diff format's timestamps are formatted differently in legacy
     mode.  By default, diff does not include nanoseconds or a timezone in
     unified diff timestamps.  In legacy mode, nanoseconds and a timezone are
     both included.  Note that patch(1) may not be able to process timestamps
     in the legacy format.

     For more information about legacy mode, see compat(5).

SEE ALSO
     cmp(1), comm(1), diff3(1), ed(1), patch(1), pr(1), sdiff(1), compat(5)

     James W. Hunt and M. Douglas McIlroy, “An Algorithm for Differential File
     Comparison”, Computing Science Technical Report, Bell Laboratories 41,
     June 1976.

STANDARDS
     The diff utility is compliant with the IEEE Std 1003.1-2008 (“POSIX.1”)
     specification.

     The flags [-AaDdIiLlNnPpqSsTtwXxy] are extensions to that specification.

HISTORY
     A diff command appeared in Version 6 AT&T UNIX.

     libdiff was imported from the Game of Trees version control system and
     default algorithm was changed to Myers for FreeBSD 15.

macOS 15.2                     February 26, 2024                    macOS 15.2