NAME

      diff - find differences between two files


SYNOPSIS

      diff [options] from-file to-file


DESCRIPTION

      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 -.

    Options
      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           combined with -c or -u.  This option is obsolete.  For proper
           operation, patch typically needs at least two lines of context.

      -a   Treat all files as text and compare them line-by-line, even if
           they do not seem to be text.

      -b   Ignore changes in amount of white space.



      -B   Ignore changes that just insert or delete blank lines.

      --brief
           Report only whether the files differ, not the details of the
           differences.

      -c   Use the context output format.

      -C lines
      --context[=lines]
           Use the context output format, showing lines (an integer) lines
           of context, or three if lines is not given.  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.

      -d   Change the algorithm to perhaps find a smaller set of changes.
           This makes diff slower (sometimes much slower).

      -D name
           Make merged if-then-else format output, conditional on the
           preprocessor macro name.

      -e
      --ed Make output that is a valid ed script.

      --exclude=pattern
           When comparing directories, ignore files and subdirectories whose
           basenames match pattern.

      --exclude-from=file
           When comparing directories, ignore files and subdirectories whose
           basenames match any pattern contained in file.

      --expand-tabs
           Expand tabs to spaces in the output, to preserve the alignment of
           tabs in the input files.

      -f   Make output that looks vaguely like an ed script but has changes
           in the order they appear in the file.

      -F regexp
           In context and unified format, for each hunk of differences, show
           some of the last preceding line that matches regexp.

      --forward-ed
           Make output that looks vaguely like an ed script but has changes


           in the order they appear in the file.

      -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.

      --horizon-lines=lines
           Do not discard the last lines lines of the common prefix and the
           first lines lines of the common suffix.

      -i   Ignore changes in case; consider upper- and lower-case letters
           equivalent.

      -I regexp
           Ignore changes that just insert or delete lines that match
           regexp.

      --ifdef=name
           Make merged if-then-else format output, conditional on the
           preprocessor macro name.

      --ignore-all-space
           Ignore white space when comparing lines.

      --ignore-blank-lines
           Ignore changes that just insert or delete blank lines.

      --ignore-case
           Ignore changes in case; consider upper- and lower-case to be the
           same.

      --ignore-matching-lines=regexp
           Ignore changes that just insert or delete lines that match
           regexp.

      --ignore-space-change
           Ignore changes in amount of white space.

      --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.

      -l   Pass the output through pr to paginate it.

      -L label
      --label=label


           Use label instead of the file name in the context format and
           unified format headers.

      --left-column
           Print only the left column of two common lines in side by side
           format.

      --line-format=format
           Use format to output all input lines in in-then-else format.

      --minimal
           Change the algorithm to perhaps find a smaller set of changes.
           This makes diff slower (sometimes much slower).

      -n   Output RCS-format diffs; like -f except that each command
           specifies the number of lines affected.

      -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.

      --new-group-format=format
           Use format to output a group of lines taken from just the second
           file in if-then-else format.

      --new-line-format=format
           Use format to output a line taken from just the second file in
           if-then-else format.

      --old-group-format=format
           Use format to output a group of lines taken from just the first
           file in if-then-else format.

      --old-line-format=format
           Use format to output a line taken from just the first file in
           if-then-else format.

      -p   Show which C function each change is in.

      -P   When comparing directories, if a file appears only in the second
           directory of the two, treat it as present but empty in the other.

      --paginate
           Pass the output through pr to paginate it.

      -q   Report only whether the files differ, not the details of the
           differences.



      -r   When comparing directories, recursively compare any
           subdirectories found.

      --rcs
           Output RCS-format diffs; like -f except that each command
           specifies the number of lines affected.

      --recursive
           When comparing directories, recursively compare any
           subdirectories found.

      --report-identical-files
      -s   Report when two files are the same.

      -S file
           When comparing directories, start with the file file.  This is
           used for resuming an aborted comparison.

      --sdiff-merge-assist
           Print extra information to help sdiff.  sdiff uses this option
           when it runs diff.  This option is not intended for users to use
           directly.

      --show-c-function
           Show which C function each change is in.

      --show-function-line=regexp
           In context and unified format, for each hunk of differences, show
           some of the last preceding line that matches regexp.

      --side-by-side
           Use the side by side output format.

      --speed-large-files
           Use heuristics to speed handling of large files that have
           numerous scattered small changes.

      --starting-file=file
           When comparing directories, start with the file file.  This is
           used for resuming an aborted comparison.

      --suppress-common-lines
           Do not print common lines in side by side format.

      -t   Expand tabs to spaces in the output, to preserve the alignment of
           tabs in the input files.

      -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.

      --text
           Treat all files as text and compare them line-by-line, even if
           they do not appear to be text.

      -u   Use the unified output format.

      --unchanged-group-format=format
           Use format to output a group of common lines taken from both
           files in if-then-else format.

      --unchanged-line-format=format
           Use format to output a line common to both files in if-then-else
           format.

      --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.

      -U lines
      --unified[=lines]
           Use the unified output format, showing lines (an integer) lines
           of context, or three if lines is not given.  For proper
           operation, patch typically needs at least two lines of context.

      -v
      --version
           Output the version number of diff.

      -w   Ignore white space when comparing lines.

      -W columns
      --width=columns
           Use an output width of columns in side by side format.

      -x pattern
           When comparing directories, ignore files and subdirectories whose
           basenames match pattern.

      -X file
           When comparing directories, ignore files and subdirectories whose
           basenames match any pattern contained in file.

      -y   Use the side by side output format.


SEE ALSO

      cmp(1), comm(1), diff3(1), ed(1), patch(1), pr(1), sdiff(1).




DIAGNOSTICS

      An exit status of 0 means no differences were found, 1 means some
      differences were found, and 2 means trouble.