PHP readfile Function

last modified April 3, 2025

The PHP readfile function reads a file and writes it to the output buffer. It's efficient for file downloads and serving static files directly.

Basic Definition

The readfile function reads a file and writes it to the output buffer. It returns the number of bytes read or false on failure.

Syntax: readfile(string $filename, bool $use_include_path = false, resource $context = ?): int|false. The function is binary-safe.

Basic readfile Example

This shows the simplest usage of readfile to output a file's contents.

basic_readfile.php

<?php

declare(strict_types=1);

$file = "example.txt";
$bytes = readfile($file);

echo "\nRead $bytes bytes";

This reads "example.txt" and outputs its contents. The function returns the number of bytes read, which we display after the file contents.

File Download Example

readfile is commonly used for file downloads with proper headers.

file_download.php

<?php

declare(strict_types=1);

$file = "document.pdf";
header("Content-Type: application/pdf");
header("Content-Disposition: attachment; filename=\"" . basename($file) . "\"");

readfile($file);
exit;

This sends PDF file as a download with appropriate headers. The browser will prompt the user to save the file rather than displaying it.

Checking File Existence

It's good practice to check if the file exists before attempting to read it.

file_exists.php

<?php

declare(strict_types=1);

$file = "data.txt";

if (file_exists($file)) {
    readfile($file);
} else {
    echo "File not found";
}

This checks for file existence first, preventing warnings if the file is missing. The file_exists function is used for the check.

Using include_path

The second parameter allows searching for files in the include path.

include_path.php

<?php

declare(strict_types=1);

$file = "config.ini";
$bytes = readfile($file, true);

if ($bytes === false) {
    echo "Failed to read file";
}

When true, the second parameter makes PHP search for the file in the include path. This is useful for files that might be in different locations.

Stream Context Example

The third parameter allows using a custom stream context for special operations.

stream_context.php

<?php

declare(strict_types=1);

$context = stream_context_create([
    "http" => [
        "method" => "GET",
        "header" => "Accept-language: en\r\n"
    ]
]);

$file = "http://example.com/data.txt";
$bytes = readfile($file, false, $context);

if ($bytes !== false) {
    echo "\nSuccessfully read $bytes bytes";
}

This demonstrates reading a remote file with custom HTTP headers. The stream context modifies how the file is accessed, adding language preferences.

Best Practices

Security: Validate file paths to prevent directory traversal.
Memory: Use for large files as it doesn't load entire file into memory.
Headers: Set appropriate Content-Type for proper handling.
Error Handling: Always check the return value for errors.
Permissions: Ensure PHP has read access to target files.

Source

PHP readfile Documentation

This tutorial covered the PHP readfile function with practical examples showing its usage in different scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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