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 stan-
    dard 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 corre-
    sponding files in both directories, in alphabetical order; this compar-
    ison 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 remain-
    ing 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 pre-
    ceded by -, and the other of which is a long name preceded by --. Mul-
    tiple single letter options (unless they take an argument) can be com-
    bined 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    is combined with -c or -u. This option is obsolete.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 opera-
    tion, 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 pre-
    processor 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 com-
    patibility.

    -H   Use heuristics to speed handling of large files that have numer-
    ous 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 reg-
    exp.

    --ifdef=name
    Make merged if-then-else format output, conditional on the pre-
    processor 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 reg-
    exp.

    --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 speci-
    fies the number of lines affected.

    -N
    --new-file
    In directory comparison, if a file is found in only one direc-
    tory, 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 subdirecto-
    ries found.

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

    --recursive
    When comparing directories, recursively compare any subdirecto-
    ries 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.

    --from-file=file
    Compare file to all operands. file can be a directory.

    --to-file=file
    Compare all operands to file. file can be a directory.

    --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 numer-
    ous 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 opera-
    tion, 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 dif-
    ferences were found, and 2 means trouble.