Git-compatible line diff for PHP
A port of Git's default diff, indent heuristic included, plus a unified diff renderer, with no runtime dependencies.

composer require php-forge/diff:^0.1

LineDiffer implements PHPForge\Diff\DifferInterface. diff() splits both strings on "\n" and returns an ordered list of DiffLine objects, each tagged with a DiffOp:

• DiffOp::Remove: the line exists only in $old.
• DiffOp::Add: the line exists only in $new.
• DiffOp::Context: the line exists on both sides.

Every input line appears exactly once, so dropping the Add lines reconstructs $old and dropping the Remove lines reconstructs $new.

use PHPForge\Diff\{DiffOp, LineDiffer};

$old = "apple\nbanana\ncherry";
$new = "apple\nblueberry\ncherry";

foreach ((new LineDiffer())->diff($old, $new) as $line) {
    echo match ($line->op) {
        DiffOp::Context => ' ',
        DiffOp::Remove => '-',
        DiffOp::Add => '+',
    } . $line->line . "\n";
}

 apple
-banana
+blueberry
 cherry

UnifiedDiffRenderer turns two texts into a unified diff in Git's format, hunk headers and function context included, without the diff --git and index lines.

use PHPForge\Diff\UnifiedDiffRenderer;

$old = "apple\nbanana\ncherry\n";
$new = "apple\nblueberry\ncherry\n";

echo (new UnifiedDiffRenderer())->render($old, $new, 'a/fruit.txt', 'b/fruit.txt');

--- a/fruit.txt
+++ b/fruit.txt
@@ -1,3 +1,3 @@
 apple
-banana
+blueberry
 cherry

N and M are the line counts of $old and $new, and D is the edit distance. Like Git, LineDiffer favours readable scripts over the shortest one, so its edit count is not always minimal. Unlike Git, it has no cost limit, so on very expensive inputs its script can differ from Git's. See the algorithms guide for the pipeline and its trade-offs.

• 📚 Installation guide
• 🧮 Algorithms guide
• 💡 Usage examples
• 🧪 Testing guide
• 🤖 AI assistance

AI agents: read the documentation index and fetch the Markdown version of a page by appending index.md to its URL. The AI agents guide covers skill installation, client setup and verification.

• 🤖 php-forge-diff skill: Line edit scripts and unified diffs.

If hosted documentation does not match the installed revision or is unavailable, use the repository guides, the skill source, the source PHPDoc and the changelog.