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DIFF(1)                            GNU Tools                           DIFF(1)

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              is combined with -c or -u.  This option is obsolete.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.  For more details on
              what can be specified in the format string, consult the info
              documentation of diff .

       -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.

       -o     Use the old traditional output 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.

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

       -r

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

       -s

       --report-identical-files
              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 horizontal 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.

RETURN VALUE
       diff returns 0 if the files are identical or 1 if the files differ.  If
       one or both of the files cannot be opened, then the return value is set
       to 2.

ENVIRONMENT
       The environment variable DIFF_OPTIONS can hold a set of default options
       for diff.  These options are interpreted first and can be overwritten
       by explicit command line parameters.

EXAMPLES
       To save to a file some changes that you have made to your local source
       tree (possibly including new files), which you would like to show to
       others (perhaps using the send-pr(1) program), you could type

       diff -crN foo.orig foo >foo.diff

       where foo.orig and foo might be directory hierarchies or single files.

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.

GNU Tools                          22sep1993                           DIFF(1)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ENVIRONMENT | EXAMPLES | SEE ALSO | DIAGNOSTICS

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