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})/". With either of these regular
expressions, this sentence, for example, would be split up into the following
tokens:
my @words = (
'With ',
'either ',
'of ',
'these ',
'regular ',
"expressions,\n",
'this ',
'sentence, ',
'for ',
'example, ',
'would ',
'be ',
'split ',
'up ',
'into ',
'the ',
'following ',
'tokens:'
);
Note that this allows the tokens to include any spacing or punctuation after
each word. So it's not just comparing words, but word-like 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-punctation 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 charaters (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.
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 repository at the following address:
<
https://svn.kineticode.com/Text-WordDiff/trunk/>
Patches against Text::WordDiff are welcome. Please send bug reports to
<bug-text-worddiff@rt.cpan.org>.
Author¶
David Wheeler <david@kineticode.com>
Copyright and License¶
Copyright (c) 2005-2008 David Wheeler. Some Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.