oracular (3) Text::WordDiff.3pm.gz
Name
Text::WordDiff - Track changes between documents
Synopsis
use Text::WordDiff;
my $diff = word_diff 'file1.txt', 'file2.txt', { STYLE => 'HTML' };
my $diff = word_diff \$string1, \$string2, { STYLE => 'ANSIColor' };
my $diff = word_diff \*FH1, \*FH2; \%options;
my $diff = word_diff \&reader1, \&reader2;
my $diff = word_diff \@records1, \@records2;
# May also mix input types:
my $diff = word_diff \@records1, 'file_B.txt';
Description
This module is a variation on the lovely Text::Diff module. Rather than generating traditional line-
oriented diffs, however, it generates word-oriented diffs. This can be useful for tracking changes in
narrative documents or documents with very long lines. To diff source code, one is still best off using
Text::Diff. But if you want to see how a short story changed from one version to the next, this module
will do the job very nicely.
What is a Word?
I'm glad you asked! Well, sort of. It's a really hard question to answer. I consulted a number of
sources, but really just did my best to punt on the question by reformulating it as, "How do I split text
up into individual words?" The short answer is to split on word boundaries. However, every word has two
boundaries, one at the beginning and one at the end. So splitting on "/\b/" didn't work so well. What I
really wanted to do was to split on the beginning of every word. Fortunately, _Mastering Regular
Expressions_ has a recipe for that: "/(?<!\w)(?=\w)/". I've borrowed this regular expression for use in
Perls before 5.6.x, but go for the Unicode variant in 5.6.0 and newer: "/(?<!\p{IsWord})(?=\p{IsWord})/".
Adding some additional controls for punctuation and control characters, this sentence, for example, would
be split up into the following tokens:
my @words = (
"Adding ",
"some ",
"additional ",
"controls",
"\n",
"for ",
"punctuation ",
"and ",
"control ",
"characters",
", ",
"this ",
"sentence",
", ",
"for ",
"example",
", ",
"would ",
"be",
"\n",
"split ",
"up ",
"into ",
"the ",
"following ",
"tokens",
":",
);
So it's not just comparing words, but word-like tokens and control/punctuation tokens. This makes sense
to me, at least, as the diff is between these tokens, and thus leads to a nice word-and-space-and-
punctuation type diff. It's not unlike what a word processor might do (although a lot of them are
character-based, but that seemed a bit extreme--feel free to dupe this module into Text::CharDiff!).
Now, I acknowledge that there are localization issues with this approach. In particular, it will fail
with Chinese, Japanese, and Korean text, as these languages don't put non-word characters between words.
Ideally, Test::WordDiff would then split on every character (since a single character often equals a
word), but such is not the case when the "utf8" flag is set on a string. For example, This simple
script:
use strict;
use utf8;
use Data::Dumper;
my $string = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';
my @tokens = split /(?<!\p{IsWord})(?=\p{IsWord})/msx, $string;
print Dumper \@tokens;
Outputs:
$VAR1 = [
"\x{bf08}\x{bf09}\x{bf18}\x{bf19}\x{bf1b}\x{bf1c}\x{bf1d}\x{bf40}\x{bf41}\x{bf44}\x{bf48}\x{bf50}\x{bf51}\x{bf55}\x{bf94}\x{bfb0}\x{bfc5}\x{bfcc}\x{bfcd}\x{bfd0}\x{bfd4}\x{bfdc}\x{bfdf}\x{bfe1}\x{c03c}\x{c051}\x{c058}\x{c05c}\x{c060}\x{c068}\x{c069}\x{c090}"
];
Not so useful. It seems to be less of a problem if the "use utf8;" line is commented out, in which case
we get:
$VAR1 = [
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'X',
'?',
'?X',
'X',
'X',
'X',
'X',
'X',
'X'
];
Someone whose more familiar with non-space-using languages will have to explain to me how I might be able
to duplicate this pattern within the scope of "use utf8;", seing as it may very well be important to have
it on in order to ensure proper character semantics.
However, if my word tokenization approach is just too naive, and you decide that you need to take a
different approach (maybe use Lingua::ZH::Toke or similar module), you can still use this module; you'll
just have to tokenize your strings into words yourself, and pass them to word_diff() as array references:
word_diff \@my_words1, \@my_words2;
Options
word_diff() takes two arguments from which to draw input and an optional hash reference of options to
control its output. The first two arguments contain the data to be diffed, and each may be in the form of
any of the following (that is, they can be in two different formats):
• String
A bare scalar will be assumed to be a file name. The file will be opened and split up into words.
word_diff() will also "stat" the file to get the last modified time for use in the header, unless the
relevant option ("MTIME_A" or "MTIME_B") has been specified explicitly.
• Scalar Reference
A scalar reference will be assumed to refer to a string. That string will be split up into words.
• Array Reference
An array reference will be assumed to be a list of words.
• File Handle
A glob or IO::Handle-derived object will be read from and split up into its constituent words.
The optional hash reference may contain the following options. Additional options may be specified by the
formattting class; see the specific class for details.
• STYLE
"ANSIColor", "HTML" or an object or class name for a class providing "file_header()",
"hunk_header()", "same_items()", "delete_items()", "insert_items()", "hunk_footer()" and
"file_footer()" methods. Defaults to "ANSIColor" for nice display of diffs in an ANSI Color-
supporting terminal.
If the package indicated by the "STYLE" has no "new()" method, "word_diff()" will load it
automatically (lazy loading). It will then instantiate an object of that class, passing in the
options hash reference with which the formatting class can initialize the object.
Styles may be specified as class names ("STYLE => "My::Foo""), in which case they will be
instantiated by calling the "new()" construcctor and passing in the options hash reference, or as
objects ("STYLE => My::Foo->new").
The simplest way to implement your own formatting style is to create a new class that inherits from
Text::WordDiff::Base, wherein the "new()" method is already provided, and the "file_header()" returns
a Unified diff-style header. All of the other formatting methods simply return empty strings, and are
therefore ripe for overriding.
• FILENAME_A, MTIME_A, FILENAME_B, MTIME_B
The name of the file and the modification time "files" in epoch seconds. Unless a defined value is
specified for these options, they will be filled in for each file when word_diff() is passed a
filename. If a filename is not passed in and "FILENAME_A" and "FILENAME_B" are not defined, the
header will not be printed by the base formatting base class.
• OUTPUT
The method by which diff output should be, well, 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 "OUTPUT" is not defined, word_diff() will simply return the diff as a string. If "OUTPUT" is a
code reference, it will be called once with the file header, once for each hunk body, and once for
each piece of content. If "OUTPUT" is an IO::Handle-derived object, output will be sent to that
handle.
• FILENAME_PREFIX_A, FILENAME_PREFIX_B
The string to print before the filename in the header. Defaults are "---", "+++".
• DIFF_OPTS
A hash reference to be passed as the options to "Algorithm::Diff->new". See Algorithm::Diff for
details on available options.
Formatting Classes
Text::WordDiff comes with two formatting classes:
Text::WordDiff::ANSIColor
This is the default formatting class. It emits a header and then the diff content, with deleted text
in bodfaced red and inserted text in boldfaced green.
Text::WordDiff::HTML
Specify "STYLE => 'HTML'" to take advantage of this formatting class. It outputs the diff content as
XHTML, with deleted text in "<del>" elements and inserted text in "<ins>" elements.
To implement your own formatting class, simply inherit from Text::WordDiff::Base and override its methods
as necssary. By default, only the "file_header()" formatting method returns a value. All others simply
return empty strings, and are therefore ripe for overriding:
package My::WordDiff::Format;
use base 'Text::WordDiff::Base';
sub file_footer { return "End of diff\n"; }
The methods supplied by the base class are:
"new()"
Constructs and returns a new formatting object. It takes a single hash reference as its argument, and
uses it to construct the object. The nice thing about this is that if you want to support other
options in your formatting class, you can just use them in the formatting object constructed by the
Text::WordDiff::Base class and document that they can be passed as part of the options hash refernce
to word_diff().
"file_header()"
Called once for a single call to "word_diff()", this method outputs the header for the whole diff.
This is the only formatting method in the base class that returns anything other than an empty
string. It collects the filenames from "filname_a()" and "filename_b()" and, if they're defined, uses
the relevant prefixes and modification times to return a unified diff-style header.
"hunk_header()"
This method is called for each diff hunk. It should output any necessary header for the hunk.
"same_items()"
This method is called for items that have not changed between the two sequnces being compared. The
unchanged items will be passed as a list to the method.
"delete_items"
This method is called for items in the first sequence that are not present in the second sequcne. The
deleted items will be passed as a list to the method.
"insert_items"
This method is called for items in the second sequence that are not present in the first sequcne. The
inserted items will be passed as a list to the method.
"hunk_footer"
This method is called at the end of a hunk. It should output any necessary content to close out the
hunk.
"file_footer()"
This method is called once when the whole diff has been procssed. It should output any necessary
content to close out the diff file.
"filename_a"
This accessor returns the value specified for the "FILENAME_A" option to word_diff().
"filename_b"
This accessor returns the value specified for the "FILENAME_B" option to word_diff().
"mtime_a"
This accessor returns the value specified for the "MTIME_A" option to word_diff().
"mtime_b"
This accessor returns the value specified for the "MTIME_B" option to word_diff().
"filename_prefix_a"
This accessor returns the value specified for the "FILENAME_PREFIX_A" option to word_diff().
"filename_prefix_b"
This accessor returns the value specified for the "FILENAME_PREFIX_B" option to word_diff().
See Also
Text::Diff
Inspired the interface and implementation of this module. Thanks Barry!
Text::ParagraphDiff
A module that attempts to diff paragraphs and the words in them.
Algorithm::Diff
The module that makes this all possible.
Support
This module is stored in an open GitHub repository <http://github.com/theory/text-worddiff/>. Feel free to fork and contribute! Please file bug reports via GitHub Issues <http://github.com/theory/text-worddiff/issues/> or by sending mail to bug-Text-WordDiff@rt.cpan.org <mailto:bug-Text-WordDiff@rt.cpan.org>.
Author
David E. Wheeler <david@justatheory.com> Currently maintained by the developers of The Perl Shop <tps@cpan.org>.
Copyright and License
Copyright (c) 2005-2011 David E. Wheeler. Some Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.