DIFF string comparison for PHP

Class used to compare differences between two strings using a DIFF implementation, with the possibility to render the diff to HTML with highlighting.

Requirements

• PHP 8.4+
• Composer

Installation

Require via composer:

composer require mistralys/text-diff

Or clone it locally via GIT, or download any of the available releases.

Usage

Comparing strings

use Mistralys\Diff\Diff;

$diff = Diff::compareStrings('String 1', 'String 2');

Comparing files

use Mistralys\Diff\Diff;

$diff = Diff::compareFiles('/path/to/file1', '/path/to/file2');

Once the diff instance has been created, choose any of the toXXX methods to retrieve the diff in your preferred format.

Important: Each Diff instance is single-use. All render methods (toString, toHTML, toHTMLTable, toArray) call the internal diff engine which clears itself after the first run. Only call one render method per instance; create a new instance for each render.

use Mistralys\Diff\Diff;

// Each call gets its own instance:
$string = Diff::compareFiles('/path/to/file1', '/path/to/file2')->toString();
$html   = Diff::compareFiles('/path/to/file1', '/path/to/file2')->toHTML();
$table  = Diff::compareFiles('/path/to/file1', '/path/to/file2')->toHTMLTable();
$array  = Diff::compareFiles('/path/to/file1', '/path/to/file2')->toArray();

Changing the comparison mode

By default, the comparison will be made per line. It can be changed to be done on a per-character basis.

Pass true as the third argument to the factory method:

use Mistralys\Diff\Diff;

$diff = Diff::compareFiles('/path/to/file1', '/path/to/file2', true);

Or use the fluent setter on an existing instance:

use Mistralys\Diff\Diff;

$diff = Diff::compareFiles('/path/to/file1', '/path/to/file2');
$diff->setCompareCharacters(true);

HTML Highlighting

The toHTML and toHTMLTable methods support highlighting the changes with the integrated CSS styles. To insert these, use the Styler class: it offers several ways to access the CSS.

use Mistralys\Diff\Diff;

$diff = Diff::compareFiles('/path/to/file1', '/path/to/file2');
$styler = Diff::createStyler();

From here, use any of the styler's methods according to your project's needs.

use Mistralys\Diff\Diff;

$styler = Diff::createStyler();

$css  = $styler->getCSS();                          // raw CSS string
$tag  = $styler->getStyleTag();                     // CSS wrapped in a <style> tag
$path = $styler->getStylesheetPath();               // absolute path to the stylesheet file
$url  = $styler->getStylesheetURL('/vendor');       // URL to the file, given the vendor folder URL
$link = $styler->getStylesheetTag('/vendor');       // a full <link rel="stylesheet"> tag

For example, to show a highlighted diff with inline styles:

use Mistralys\Diff\Diff;

$diff = Diff::compareStrings('String 1', 'String 2');

echo Diff::createStyler()->getStyleTag();
echo $diff->toHTML();

Releasing diff instances

When a Diff instance is no longer needed and you want to free its memory explicitly, call dispose():

use Mistralys\Diff\Diff;

$diff = Diff::compareStrings('String 1', 'String 2');
$html = $diff->toHTML();

$diff->dispose();

Note: Calling any render method after dispose() will throw a DiffException. Always render before disposing.

Running the Examples

The example/ folder demonstrates every renderer — inline HTML, table HTML, plain text, and character-level comparisons — against both inline strings and sample text files.

Static preview (no server required)

A pre-built HTML file is included at example/dist/index.html. Open it directly in your browser for a quick overview.

To regenerate it after making changes:

composer install  # only needed once after cloning
composer build

The output is written to example/dist/index.html.

Live example (PHP web server)

If you want to run the PHP version directly:

composer install  # only needed once after cloning
php -S localhost:8000

Then open http://localhost:8000/example/ in your browser.

Credits

The original Diff class was developed by Kate Morley. Compared to her version, this has been reworked extensively. The core mechanism stays the same, but updated for PHP7, and split up into subclasses to make it easier to extend and maintain. The static comparison methods are still there, but they return a diff instance now.

The original project homepage can be found here:

http://code.iamkate.com/php/diff-implementation/

Kate has since removed the library from her site, but I am keeping this here as reference.