PHP script to generate a file with random data of given name and size?

Do you really need so much variation in filesize that you need a PHP script? I'd just create test files of varying sizes via the command line and use them in my unit tests. Unless the filesize itself is likely to cause a bug, it would seem you're over-engineering here...

To create a file in Windows;

fsutil file createnew d:\filepath\filename.txt 1048576

in Linux;

dd if=/dev/zero of=filepath/filename.txt bs=10000000 count=1

if is the file source (in this case nothing), of is the output file, bs is the final filesize, count defines how many blocks you want to copy.

To start you could try something like this:

function generate_file($file_name, $size_in_bytes)
{
   $data = str_repeat(rand(0,9), $size_in_bytes);
   file_put_contents($file_name, $data); //writes $data in a file   
}

This creates file filled up with a random digit (0-9).

generate_file() from @Marco Demaio caused this below when generating 4GB file.

Warning: str_repeat(): Result is too big, maximum 2147483647 allowed in /home/xxx/test_suite/handler.php on line 38

I found below function from php.net and it's working like charm. I have tested it upto

17.6 TB (see update below)

in less than 3 seconds.

function CreatFileDummy($file_name,$size = 90294967296 ) {   
// 32bits 4 294 967 296 bytes MAX Size
    $f = fopen('dummy/'.$file_name, 'wb');
    if($size >= 1000000000)  {
        $z = ($size / 1000000000);       
        if (is_float($z))  {
            $z = round($z,0);
            fseek($f, ( $size - ($z * 1000000000) -1 ), SEEK_END);
            fwrite($f, "\0");
        }       
        while(--$z > -1) {
            fseek($f, 999999999, SEEK_END);
            fwrite($f, "\0");
        }
    }
    else {
        fseek($f, $size - 1, SEEK_END);
        fwrite($f, "\0");
    }
    fclose($f);

return true;
}

Update:

I was trying to hit 120TB, 1200 TB and more but filesize was limited to 17.6 TB. After some googling I found that it is max_volume_size for ReiserFS file system which was on my server. May be PHP can handle 1200TB also in just few seconds. :)

generate_file() from "Marco Demaio" is not memory friendly so I created file_rand().

function file_rand($filename, $filesize) {
    if ($h = fopen($filename, 'w')) {
        if ($filesize > 1024) {
            for ($i = 0; $i < floor($filesize / 1024); $i++) {
                fwrite($h, bin2hex(openssl_random_pseudo_bytes(511)) . PHP_EOL);
            }
            $filesize = $filesize - (1024 * $i);
        }
        $mod = $filesize % 2;
        fwrite($h, bin2hex(openssl_random_pseudo_bytes(($filesize - $mod) / 2)));
        if ($mod) {
            fwrite($h, substr(uniqid(), 0, 1));
        }
        fclose($h);
        umask(0000);
        chmod($filename, 0644);
    }
}

As you can see linebreaks are added every 1024 bytes to avoid problems with functions that are limited to 1024-9999 bytes. e.g. fgets() with <= PHP 4.3. And it makes it easier to open the file with an text editor having the same issue with super long lines.