How to Write to a File with file_put_contents()

Table Of Contents

• Quick Implementation
• The Answer

Quick Implementation

The issue is needing to write data to files efficiently. You can solve this by using file_put_contents() with appropriate flags:

<?php

// Basic file writing
$data = "Hello, World!\nThis is line 2.";
file_put_contents('output.txt', $data);

// Append to existing file
$newData = "\nAppended line";
file_put_contents('output.txt', $newData, FILE_APPEND | LOCK_EX);

// Write array data as JSON
$users = [
    ['id' => 1, 'name' => 'John', 'email' => 'john@example.com'],
    ['id' => 2, 'name' => 'Jane', 'email' => 'jane@example.com']
];
file_put_contents('users.json', json_encode($users, JSON_PRETTY_PRINT));

// Write CSV data
function writeArrayToCsv(array $data, string $filename): bool {
    if (empty($data)) {
        return false;
    }
    
    $output = fopen('php://temp', 'r+');
    
    // Write header
    fputcsv($output, array_keys($data[0]));
    
    // Write data rows
    foreach ($data as $row) {
        fputcsv($output, $row);
    }
    
    rewind($output);
    $csvContent = stream_get_contents($output);
    fclose($output);
    
    return file_put_contents($filename, $csvContent) !== false;
}

// Configuration file writer
function saveConfig(array $config, string $filename): bool {
    $content = "<?php\n// Auto-generated configuration file\n\nreturn [\n";
    
    foreach ($config as $key => $value) {
        $content .= "    '$key' => " . var_export($value, true) . ",\n";
    }
    
    $content .= "];\n";
    
    return file_put_contents($filename, $content, LOCK_EX) !== false;
}

// Log file writer with timestamp
function writeLog(string $message, string $level = 'INFO', string $logFile = 'app.log'): void {
    $timestamp = date('Y-m-d H:i:s');
    $logEntry = "[$timestamp] [$level] $message\n";
    
    file_put_contents($logFile, $logEntry, FILE_APPEND | LOCK_EX);
}

// Atomic file writing (safer for concurrent access)
function atomicWrite(string $filename, string $content): bool {
    $tempFile = $filename . '.tmp.' . uniqid();
    
    try {
        if (file_put_contents($tempFile, $content, LOCK_EX) === false) {
            return false;
        }
        
        if (!rename($tempFile, $filename)) {
            unlink($tempFile);
            return false;
        }
        
        return true;
    } catch (Exception $e) {
        if (file_exists($tempFile)) {
            unlink($tempFile);
        }
        throw $e;
    }
}

// Error handling wrapper
function safeFileWrite(string $filename, string $content, int $flags = 0): bool {
    // Ensure directory exists
    $directory = dirname($filename);
    if (!is_dir($directory)) {
        if (!mkdir($directory, 0755, true)) {
            throw new RuntimeException("Cannot create directory: $directory");
        }
    }
    
    // Check permissions
    if (file_exists($filename) && !is_writable($filename)) {
        throw new RuntimeException("File is not writable: $filename");
    }
    
    if (!is_writable($directory)) {
        throw new RuntimeException("Directory is not writable: $directory");
    }
    
    $result = file_put_contents($filename, $content, $flags);
    
    if ($result === false) {
        throw new RuntimeException("Failed to write to file: $filename");
    }
    
    return true;
}

// Usage examples
try {
    // Write simple text
    file_put_contents('data/output.txt', 'Sample content');
    
    // Save user data as JSON
    $userData = ['name' => 'John', 'age' => 30];
    file_put_contents('data/user.json', json_encode($userData));
    
    // Append to log
    writeLog('User logged in', 'INFO');
    writeLog('Failed login attempt', 'WARNING');
    
    // Write CSV
    $csvData = [
        ['name' => 'John', 'age' => 30, 'city' => 'New York'],
        ['name' => 'Jane', 'age' => 25, 'city' => 'Los Angeles']
    ];
    writeArrayToCsv($csvData, 'data/users.csv');
    
    // Save configuration
    $config = [
        'database_host' => 'localhost',
        'database_name' => 'myapp',
        'debug_mode' => false
    ];
    saveConfig($config, 'config/app.php');
    
    // Atomic write for critical data
    atomicWrite('critical-data.txt', 'Important information');
    
} catch (RuntimeException $e) {
    echo "Error: " . $e->getMessage();
}

The Answer

file_put_contents() is the most straightforward way to write files:

1. Simple Syntax: One function call writes entire content
2. Automatic Handling: Creates file if it doesn't exist
3. Flag Support: Control behavior with FILE_APPEND, LOCK_EX
4. Return Value: Returns bytes written or false on failure

Common Flags:

• FILE_APPEND - Add to end of file instead of overwriting
• LOCK_EX - Acquire exclusive lock while writing
• FILE_USE_INCLUDE_PATH - Search in include path

Best Practices:

• Use LOCK_EX for concurrent access safety
• Check return value for error handling
• Ensure directory permissions before writing
• Use atomic writes for critical data

This approach handles most file writing needs efficiently and safely.