PHP fread Function

last modified April 3, 2025

The PHP fread function reads from an open file pointer. It's a binary-safe function that reads up to a specified number of bytes.

Basic Definition

The fread function reads from a file pointer. It takes two parameters: the file handle and the length to read.

Syntax: fread(resource $stream, int $length): string|false. The function returns the read string or false on failure.

Basic fread Example

This shows the simplest usage of fread to read a file.

basic_fread.php

<?php

declare(strict_types=1);

$filename = "example.txt";
$handle = fopen($filename, "r");
$contents = fread($handle, filesize($filename));
fclose($handle);

echo $contents;

This reads the entire contents of example.txt. We first open the file, read it, then close the handle. Always close file handles when done.

Reading Fixed Length

fread can read a specific number of bytes from a file.

fixed_length.php

<?php

declare(strict_types=1);

$filename = "data.bin";
$handle = fopen($filename, "rb");
$chunk = fread($handle, 1024);
fclose($handle);

echo "Read " . strlen($chunk) . " bytes";

Here we read exactly 1024 bytes from a binary file. The "rb" mode ensures binary-safe reading on all platforms.

Reading Line by Line

Combine fread with other functions for line-based reading.

line_by_line.php

<?php

declare(strict_types=1);

$filename = "lines.txt";
$handle = fopen($filename, "r");

while (!feof($handle)) {
    $line = fread($handle, 4096); // Read in chunks
    echo $line;
}

fclose($handle);

This reads the file in 4096-byte chunks until EOF. For text files, consider using fgets instead for line-by-line reading.

Binary File Reading

fread is ideal for reading binary files like images.

binary_file.php

<?php

declare(strict_types=1);

$filename = "image.jpg";
$handle = fopen($filename, "rb");
$data = fread($handle, filesize($filename));
fclose($handle);

header("Content-Type: image/jpeg");
echo $data;

This reads a JPEG image and outputs it directly. The binary mode ensures no data corruption occurs during reading.

Reading with Offset

Combine fread with fseek for random access.

offset_read.php

<?php

declare(strict_types=1);

$filename = "largefile.dat";
$handle = fopen($filename, "rb");
fseek($handle, 1024); // Skip first 1KB
$data = fread($handle, 512); // Read 512 bytes
fclose($handle);

echo "Read " . strlen($data) . " bytes from offset 1024";

This demonstrates reading from a specific file offset. Useful for large files where you only need certain sections.

Best Practices

Error Handling: Always check if fopen succeeded.
Resource Cleanup: Use try-finally for handle cleanup.
Memory Limits: Be mindful when reading large files.
Binary Safety: Use "b" mode for binary files.
Performance: Choose appropriate chunk sizes.

Source

PHP fread Documentation

This tutorial covered the PHP fread 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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