Simple PHP Diff

A lightweight PHP library for fast text comparison and difference visualization. Find the quick difference between two text files and render the results in plain text or HTML format.

Key Principles

• Line-by-line comparison - Compares texts line by line with numbered output for easy change tracking
• Immutable result object - Returns a Diff object containing original, target, formatted diff, and changed line numbers
• Dual output modes - Plain text diff output and styled HTML rendering with color-coded changes
• Strict mode support - Optional strict comparison that preserves different line ending formats
• Whitespace visualization - Pretty rendering shows tabs as arrows and spaces as dots for clarity
• Zero dependencies - Pure PHP implementation requiring only PHP 8.0+

Architecture

The library consists of two main components with a clean separation of concerns:

┌─────────────────────────────────────────────────────────────┐
│                        SimpleDiff                           │
│  ┌─────────────────────────────────────────────────────┐   │
│  │  compare($left, $right, $strict)                    │   │
│  │  - Normalizes line endings (non-strict mode)        │   │
│  │  - Performs line-by-line comparison                 │   │
│  │  - Tracks changed line numbers                      │   │
│  │  - Formats output with line numbers                 │   │
│  └─────────────────────────────────────────────────────┘   │
│                           │                                 │
│                           ▼                                 │
│  ┌─────────────────────────────────────────────────────┐   │
│  │  renderDiff($diff)                                  │   │
│  │  - Converts diff to styled HTML                     │   │
│  │  - Color-codes additions (green) / removals (red)   │   │
│  └─────────────────────────────────────────────────────┘   │
└─────────────────────────────────────────────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│                          Diff                               │
│  Immutable Value Object                                     │
│  ┌─────────────────────────────────────────────────────┐   │
│  │  - original: string     (normalized left input)     │   │
│  │  - target: string       (normalized right input)    │   │
│  │  - diff: string         (formatted diff output)     │   │
│  │  - changedLines: int[]  (line numbers that changed) │   │
│  └─────────────────────────────────────────────────────┘   │
└─────────────────────────────────────────────────────────────┘

Components

SimpleDiff

The main comparison engine that processes two text inputs and generates a diff result.

Methods:

Method	Description
compare(string $left, string $right, bool $strict = false): Diff	Compares two strings and returns a Diff object
renderDiff(Diff|string $diff): string	Renders the diff as styled HTML

Comparison Process:

1. Input normalization (non-strict mode): Converts all line endings (\r\n, \r) to \n and trims whitespace
2. Line splitting: Splits both inputs into arrays by newline character
3. Line-by-line comparison: Iterates through lines, comparing original vs target
4. Output formatting: Prepends each line with status marker (+, -, or space) and line number
5. Change tracking: Records line numbers where differences occur

Diff

An immutable value object that encapsulates the comparison result.

Properties (via getters):

Property	Type	Description
original	string	The normalized left/original input text
target	string	The normalized right/target input text
diff	string	The formatted diff output with line markers
changedLines	int[]	Array of line numbers (1-indexed) that differ

String Conversion:

The Diff object implements __toString() which returns the formatted diff string, allowing direct string casting.

📦 Installation

It's best to use Composer for installation, and you can also find the package on Packagist and GitHub.

To install, simply use the command:

$ composer require baraja-core/simple-php-diff

You can use the package manually by creating an instance of the internal classes, or register a DIC extension to link the services directly to the Nette Framework.

Requirements

• PHP 8.0 or higher

Basic Usage

Simple Text Comparison

use Baraja\DiffGenerator\SimpleDiff;

$left = 'First text';
$right = 'Second text';

$diff = (new SimpleDiff)->compare($left, $right);

// Output the diff as plain text
echo '<code><pre>' . htmlspecialchars((string) $diff) . '</pre></code>';

Get Changed Line Numbers

$diff = (new SimpleDiff)->compare($left, $right);

echo 'Changed lines: ' . implode(', ', $diff->getChangedLines());

Render Diff as HTML

$simpleDiff = new SimpleDiff;
$diff = $simpleDiff->compare($left, $right);

// Returns styled HTML with color-coded changes
echo $simpleDiff->renderDiff($diff);

Output Format

Plain Text Output

The diff output uses a standardized format:

  1| unchanged line
- 2| removed·line·with·visible·spaces
+ 2| added→→→→line·with·visible·tabs
  3| another unchanged line

Format explanation:

• Lines starting with (two spaces) are unchanged
• Lines starting with - indicate content from the original (left) text
• Lines starting with + indicate content from the target (right) text
• Line numbers are right-padded and followed by |
• Spaces are rendered as · (middle dot)
• Tabs are rendered as →→→→ (four arrows)

HTML Output

The renderDiff() method generates HTML with inline styles:

<pre class="code">
<div>  1| unchanged line</div>
<div style="background:#e7acac">- 2| removed line</div>
<div style="background:#a2f19c">+ 2| added line</div>
<div>  3| another unchanged line</div>
</pre>

Color coding:

• Green background (#a2f19c): Added lines (prefixed with +)
• Red background (#e7acac): Removed lines (prefixed with -)
• No background: Unchanged lines

Visual Examples

Plain Text Diff Output

HTML Rendered Diff

Comparison Modes

Non-Strict Mode (Default)

In non-strict mode (default), the library normalizes line endings before comparison:

• Converts \r\n (Windows) to \n
• Converts \r (old Mac) to \n
• Trims leading and trailing whitespace from both inputs

This mode is ideal for comparing content where line ending differences should be ignored.

// Non-strict comparison (default)
$diff = (new SimpleDiff)->compare($left, $right);
$diff = (new SimpleDiff)->compare($left, $right, false);

Strict Mode

Strict mode preserves the original line endings and whitespace, useful when you need to detect differences in line termination characters.

// Strict comparison - preserves line endings
$diff = (new SimpleDiff)->compare($left, $right, true);

Working with the Diff Object

Accessing Original and Target Text

$diff = (new SimpleDiff)->compare($left, $right);

// Get the normalized original text
$original = $diff->getOriginal();

// Get the normalized target text
$target = $diff->getTarget();

Getting the Raw Diff String

$diff = (new SimpleDiff)->compare($left, $right);

// Using getter method
$diffString = $diff->getDiff();

// Using string casting (equivalent)
$diffString = (string) $diff;

Working with Changed Lines

$diff = (new SimpleDiff)->compare($left, $right);
$changedLines = $diff->getChangedLines();

// Example output: [2, 5, 8] - lines 2, 5, and 8 were modified
foreach ($changedLines as $lineNumber) {
    echo "Line {$lineNumber} was changed\n";
}

// Check if any changes occurred
if (count($changedLines) === 0) {
    echo "No differences found!";
}

Advanced Examples

Comparing Files

$originalFile = file_get_contents('/path/to/original.txt');
$modifiedFile = file_get_contents('/path/to/modified.txt');

$simpleDiff = new SimpleDiff;
$diff = $simpleDiff->compare($originalFile, $modifiedFile);

// Check if files are identical
if (empty($diff->getChangedLines())) {
    echo "Files are identical.";
} else {
    echo "Files differ on lines: " . implode(', ', $diff->getChangedLines());
    echo "\n\n";
    echo $diff;
}

Custom HTML Rendering

If you need custom styling, you can process the diff string yourself:

$diff = (new SimpleDiff)->compare($left, $right);

$lines = explode("\n", $diff->getDiff());
$html = '<div class="my-diff-container">';

foreach ($lines as $line) {
    $firstChar = $line[0] ?? '';
    $cssClass = match ($firstChar) {
        '+' => 'diff-added',
        '-' => 'diff-removed',
        default => 'diff-unchanged',
    };
    $html .= sprintf('<div class="%s">%s</div>', $cssClass, htmlspecialchars($line));
}

$html .= '</div>';
echo $html;

Integration with Version Control Display

function showCommitDiff(string $oldContent, string $newContent): string
{
    $simpleDiff = new SimpleDiff;
    $diff = $simpleDiff->compare($oldContent, $newContent);

    $changedCount = count($diff->getChangedLines());

    $output = "<h3>Changes: {$changedCount} line(s) modified</h3>";
    $output .= $simpleDiff->renderDiff($diff);

    return $output;
}

Author

Jan Barášek - https://baraja.cz

📄 License

baraja-core/simple-php-diff is licensed under the MIT license. See the LICENSE file for more details.