Mastering PHP’s readfile(): Quick File Output and Download Guide

In PHP, the readfile() function is a convenient way to output a file’s contents directly to the browser or another file.

Syntax:

int readfile ( string $filename [, bool $use_include_path = FALSE [, resource $context ]] )

The function takes a filename, reads the file, and outputs its content. It returns the number of bytes read, or false on failure.

Example file data.txt:

Hello, World!
I am learning PHP.

To send this file to the browser for download:

<?php
$file = 'data.txt'; // file path
if (file_exists($file)) {
    header('Content-Disposition: attachment; filename=' . basename($file)); // download header
    header('Content-type: text/plain'); // set MIME type
    readfile($file); // output file content
} else {
    echo "File does not exist.";
}
?>

The script checks that the file exists, sets appropriate HTTP headers, and then calls readfile() to output the file.

Running the script will cause the browser to download data.txt containing the file’s text. readfile() can also write a file’s contents to another file. By providing a target path as the second argument, you can copy the source file:

<?php
$sourceFile = 'data.txt'; // source file
$targetFile = 'output.txt'; // destination file
if (file_exists($sourceFile)) {
    readfile($sourceFile, $targetFile); // output to target file
} else {
    echo "File does not exist.";
}
?>

After execution, the contents of data.txt are written to output.txt. Using readfile() thus simplifies file output for both browser downloads and file copying.