NAME
    Text::Diff - Perform diffs on files and record sets

SYNOPSIS
        use Text::Diff;

        ## Mix and match filenames, strings, file handles, producer subs,
        ## or arrays of records; returns diff in a string.
        ## WARNING: can return B<large> diffs for large files.
        my $diff = diff "file1.txt", "file2.txt", { STYLE => "Context" };
        my $diff = diff \$string1,   \$string2,   \%options;
        my $diff = diff \*FH1,       \*FH2;
        my $diff = diff \&reader1,   \&reader2;
        my $diff = diff \@records1,  \@records2;

        ## May also mix input types:
        my $diff = diff \@records1,  "file_B.txt";

DESCRIPTION
    "diff()" provides a basic set of services akin to the GNU "diff"
    utility. It is not anywhere near as feature complete as GNU "diff", but
    it is better integrated with Perl and available on all platforms. It is
    often faster than shelling out to a system's "diff" executable for small
    files, and generally slower on larger files.

    Relies on Algorithm::Diff for, well, the algorithm. This may not produce
    the same exact diff as a system's local "diff" executable, but it will
    be a valid diff and comprehensible by "patch". We haven't seen any
    differences between Algorithm::Diff's logic and GNU diff's, but we have
    not examined them to make sure they are indeed identical.

    Note: If you don't want to import the "diff" function, do one of the
    following:

       use Text::Diff ();

       require Text::Diff;

    That's a pretty rare occurence, so "diff()" is exported by default.
    =head1 OPTIONS

    diff() takes two parameters from which to draw input and a set of
    options to control it's output. The options are:

    FILENAME_A, MTIME_A, FILENAME_B, MTIME_B
        The name of the file and the modification time "files"

        These are filled in automatically for each file when diff() is
        passed a filename, unless a defined value is passed in.

        If a filename is not passed in and FILENAME_A and FILENAME_B are not
        provided or "undef", the header will not be printed.

        Unused on "OldStyle" diffs.

    OFFSET_A, OFFSET_B
        The index of the first line / element. These default to 1 for all
        parameter types except ARRAY references, for which the default is 0.
        This is because ARRAY references are presumed to be data structures,
        while the others are line oriented text.

    STYLE
        "Unified", "Context", "OldStyle", or an object or class reference
        for a class providing "file_header()", "hunk_header()", "hunk()",
        "hunk_footer()" and "file_footer()" methods. The two footer()
        methods are provided for overloading only; none of the formats
        provide them.

        Defaults to "Unified" (unlike standard "diff", but Unified is what's
        most often used in submitting patches and is the most human readable
        of the three.

        If the package indicated by the STYLE has no hunk() method,
        c<diff()> will load it automatically (lazy loading). Since all such
        packages should inherit from Text::Diff::Base, this should be marvy.

        Styles may be specified as class names ("STYLE =" "Foo"), in which
        case they will be "new()"ed with no parameters, or as objects
        ("STYLE =" Foo->new>).

    CONTEXT
        How many lines before and after each diff to display. Ignored on
        old-style diffs. Defaults to 3.

    OUTPUT
        Examples and their equivalent subroutines:

            OUTPUT   => \*FOOHANDLE,   # like: sub { print FOOHANDLE shift() }
            OUTPUT   => \$output,      # like: sub { $output .= shift }
            OUTPUT   => \@output,      # like: sub { push @output, shift }
            OUTPUT   => sub { $output .= shift },

        If no "OUTPUT" is supplied, returns the diffs in a string. If
        "OUTPUT" is a "CODE" ref, it will be called once with the (optional)
        file header, and once for each hunk body with the text to emit. If
        "OUTPUT" is an IO::Handle, output will be emitted to that handle.

    FILENAME_PREFIX_A, FILENAME_PREFIX_B
        The string to print before the filename in the header. Unused on
        "OldStyle" diffs. Defaults are "---", "+++" for Unified and "***",
        "+++" for Context.

    KEYGEN, KEYGEN_ARGS
        These are passed to "traverse_sequences" in Algorithm::Diff.

    Note: if neither "FILENAME_" option is defined, the header will not be
    printed. If at one is present, the other and both MTIME_ options must be
    present or "Use of undefined variable" warnings will be generated
    (except on "OldStyle" diffs, which ignores these options).

Formatting Classes
    These functions implement the output formats. They are grouped in to
    classes so diff() can use class names to call the correct set of output
    routines and so that you may inherit from them easily. There are no
    constructors or instance methods for these classes, though subclasses
    may provide them if need be.

    Each class has file_header(), hunk_header(), hunk(), and footer()
    methods identical to those documented in the Text::Diff::Unified
    section. header() is called before the hunk() is first called, footer()
    afterwards. The default footer function is an empty method provided for
    overloading:

        sub footer { return "End of patch\n" }

    Some output formats are provided by external modules (which are loaded
    automatically), such as Text::Diff::Table. These are are documented here
    to keep the documentation simple.

  Text::Diff::Base
    Returns "" for all methods (other than "new()").

  Text::Diff::Unified
      --- A   Mon Nov 12 23:49:30 2001
      +++ B   Mon Nov 12 23:49:30 2001
      @@ -2,13 +2,13 @@
       2
       3
       4
      -5d
      +5a
       6
       7
       8
       9
      +9a
       10
       11
      -11d
       12
       13

    file_header
          $s = Text::Diff::Unified->file_header( $options );

        Returns a string containing a unified header. The sole parameter is
        the options hash passed in to diff(), containing at least:

          FILENAME_A  => $fn1,
          MTIME_A     => $mtime1,
          FILENAME_B  => $fn2,
          MTIME_B     => $mtime2

        May also contain

          FILENAME_PREFIX_A    => "---",
          FILENAME_PREFIX_B    => "+++",

        to override the default prefixes (default values shown).

    hunk_header
          Text::Diff::Unified->hunk_header( \@ops, $options );

        Returns a string containing the output of one hunk of unified diff.

    Text::Diff::Unified::hunk
          Text::Diff::Unified->hunk( \@seq_a, \@seq_b, \@ops, $options );

        Returns a string containing the output of one hunk of unified diff.

  Text::Diff::Table
      +--+----------------------------------+--+------------------------------+
      |  |../Test-Differences-0.2/MANIFEST  |  |../Test-Differences/MANIFEST  |
      |  |Thu Dec 13 15:38:49 2001          |  |Sat Dec 15 02:09:44 2001      |
      +--+----------------------------------+--+------------------------------+
      |  |                                  * 1|Changes                       *
      | 1|Differences.pm                    | 2|Differences.pm                |
      | 2|MANIFEST                          | 3|MANIFEST                      |
      |  |                                  * 4|MANIFEST.SKIP                 *
      | 3|Makefile.PL                       | 5|Makefile.PL                   |
      |  |                                  * 6|t/00escape.t                  *
      | 4|t/00flatten.t                     | 7|t/00flatten.t                 |
      | 5|t/01text_vs_data.t                | 8|t/01text_vs_data.t            |
      | 6|t/10test.t                        | 9|t/10test.t                    |
      +--+----------------------------------+--+------------------------------+

    This format also goes to some pains to highlight "invisible" characters
    on differing elements by selectively escaping whitespace:

      +--+--------------------------+--------------------------+
      |  |demo_ws_A.txt             |demo_ws_B.txt             |
      |  |Fri Dec 21 08:36:32 2001  |Fri Dec 21 08:36:50 2001  |
      +--+--------------------------+--------------------------+
      | 1|identical                 |identical                 |
      * 2|        spaced in         |        also spaced in    *
      * 3|embedded space            |embedded        tab       *
      | 4|identical                 |identical                 |
      * 5|        spaced in         |\ttabbed in               *
      * 6|trailing spaces\s\s\n     |trailing tabs\t\t\n       *
      | 7|identical                 |identical                 |
      * 8|lf line\n                 |crlf line\r\n             *
      * 9|embedded ws               |embedded\tws              *
      +--+--------------------------+--------------------------+

    See "Text::Diff::Table" for more details, including how the whitespace
    escaping works.

  Text::Diff::Context
        *** A   Mon Nov 12 23:49:30 2001
        --- B   Mon Nov 12 23:49:30 2001
        ***************
        *** 2,14 ****
          2
          3
          4
        ! 5d
          6
          7
          8
          9
          10
          11
        - 11d
          12
          13
        --- 2,14 ----
          2
          3
          4
        ! 5a
          6
          7
          8
          9
        + 9a
          10
          11
          12
          13

    Note: hunk_header() returns only "***************\n".

  Text::Diff::OldStyle
        5c5
        < 5d
        ---
        > 5a
        9a10
        > 9a
        12d12
        < 11d

    Note: no file_header().

LIMITATIONS
    Must suck both input files entirely in to memory and store them with a
    normal amount of Perlish overhead (one array location) per record. This
    is implied by the implementation of Algorithm::Diff, which takes two
    arrays. If Algorithm::Diff ever offers an incremental mode, this can be
    changed (contact the maintainers of Algorithm::Diff and Text::Diff if
    you need this; it shouldn't be too terribly hard to tie arrays in this
    fashion).

    Does not provide most of the more refined GNU diff options: recursive
    directory tree scanning, ignoring blank lines / whitespace, etc., etc.
    These can all be added as time permits and need arises, many are rather
    easy; patches quite welcome.

    Uses closures internally, this may lead to leaks on "perl" versions
    5.6.1 and prior if used many times over a process' life time.

AUTHOR
    Adam Kennedy <adamk@cpan.org>

    Barrie Slaymaker <barries@slaysys.com>

COPYRIGHT
    Some parts copyright 2009 Adam Kennedy.

    Copyright 2001 Barrie Slaymaker. All Rights Reserved.

    You may use this under the terms of either the Artistic License or GNU
    Public License v 2.0 or greater.