What is fwrite() in PHP?

fwrite() is a built-in PHP function used to write data to a file. It's one of the fundamental file handling functions in PHP for writing content to files on the server.

Syntax

fwrite(resource $handle, string $string, int $length = ?): int|false

Parameters

• $handle: A file pointer resource created by fopen()
• $string: The data to write to the file
• $length (optional): Maximum number of bytes to write

Return Value

• Returns the number of bytes written on success
• Returns false on failure

Basic Usage Examples

1. Writing to a File

<?php
// Open file for writing
$file = fopen("example.txt", "w");

if ($file) {
    // Write content to file
    $bytesWritten = fwrite($file, "Hello, World!");
    
    echo "Bytes written: " . $bytesWritten;
    
    // Close the file
    fclose($file);
} else {
    echo "Could not open file!";
}
?>

2. Appending to a File

<?php
// Open file for appending (content added to end)
$file = fopen("example.txt", "a");

if ($file) {
    fwrite($file, "\nThis is appended text.");
    fclose($file);
    echo "Content appended successfully!";
}
?>

3. Writing with Length Limit

<?php
$file = fopen("example.txt", "w");
$text = "This is a long text string";

// Write only first 10 bytes
fwrite($file, $text, 10);
// File contains: "This is a"
fclose($file);
?>

File Mode Examples

Practical Examples

1. Logging Messages

<?php
function logMessage($message) {
    $file = fopen("app.log", "a");
    if ($file) {
        $timestamp = date('Y-m-d H:i:s');
        fwrite($file, "[$timestamp] $message\n");
        fclose($file);
    }
}

logMessage("User logged in");
logMessage("File uploaded successfully");
?>

2. Writing CSV Data

<?php
function writeCSV($filename, $data) {
    $file = fopen($filename, "w");
    if ($file) {
        foreach ($data as $row) {
            fputcsv($file, $row); // fputcsv uses fwrite internally
        }
        fclose($file);
        return true;
    }
    return false;
}

$data = [
    ['Name', 'Email', 'Age'],
    ['John Doe', 'john@example.com', 30],
    ['Jane Smith', 'jane@example.com', 25]
];

writeCSV("users.csv", $data);
?>

3. File Upload Handling

<?php
if ($_FILES['file']['error'] === UPLOAD_ERR_OK) {
    $uploadedFile = $_FILES['file']['tmp_name'];
    $destination = "uploads/" . $_FILES['file']['name'];
    
    $source = fopen($uploadedFile, "r");
    $dest = fopen($destination, "w");
    
    // Copy file chunk by chunk (good for large files)
    while (!feof($source)) {
        $chunk = fread($source, 8192); // 8KB chunks
        fwrite($dest, $chunk);
    }
    
    fclose($source);
    fclose($dest);
    
    echo "File uploaded successfully!";
}
?>

Error Handling

<?php
$file = @fopen("example.txt", "w");

if (!$file) {
    die("Error: Could not open file for writing");
}

$result = fwrite($file, "Some content");

if ($result === false) {
    die("Error: Could not write to file");
}

echo "Successfully wrote $result bytes to file";
fclose($file);
?>

Best Practices

1. Always check if file opened successfully
2. Handle errors appropriately
3. Close files with fclose() when done
4. Use appropriate file modes (w, a, x, c)
5. Consider file permissions on the server
6. Use FILE_APPEND flag with file_put_contents() for simpler append operations

Alternative: file_put_contents()

For simpler write operations, you can use:

<?php
// Write to file (overwrites existing content)
file_put_contents("example.txt", "Hello World!");

// Append to file
file_put_contents("example.txt", "New line\n", FILE_APPEND);

// Lock file while writing
file_put_contents("example.txt", "Content", LOCK_EX);
?>

fwrite() gives you more control over the writing process, especially useful for large files or when you need to write data in chunks.