hexdump.php

<?php
/**
 * View any string as a hexdump.
 *
 * This is most commonly used to view binary data from streams
 * or sockets while debugging, but can be used to view any string
 * with non-viewable characters.
 *
 * @version     1.3.2
 * @author      Aidan Lister <aidan@php.net>
 * @author      Peter Waller <iridum@php.net>
 * @link        http://aidanlister.com/repos/v/function.hexdump.php
 * @param       string  $data        The string to be dumped
 * @param       bool    $htmloutput  Set to false for non-HTML output
 * @param       bool    $uppercase   Set to true for uppercase hex
 * @param       bool    $return      Set to true to return the dump
 */
function hexdump ($data, $htmloutput = false, $uppercase = false, $return = false)
{
    // Init
    $hexi   = '';
    $ascii  = '';
    $dump   = ($htmloutput === true) ? '<pre>' : '';
    $offset = 0;
    $len    = strlen($data);

    // Upper or lower case hexidecimal
    $x = ($uppercase === false) ? 'x' : 'X';

    // Iterate string
    for ($i = $j = 0; $i < $len; $i++)
    {
        // Convert to hexidecimal
        $hexi .= sprintf("%02$x ", ord($data[$i]));

        // Replace non-viewable bytes with '.'
        if (ord($data[$i]) >= 32 && ord($data[$i]) < 127) {
            $ascii .= ($htmloutput === true) ?
                            htmlentities($data[$i]) :
                            $data[$i];
        } else {
            $ascii .= '.';
        }

        // Add extra column spacing
        if ($j === 7) {
            $hexi  .= ' ';
            $ascii .= ' ';
        }

        // Add row
        if (++$j === 16 || $i === $len - 1) {
            // Join the hexi / ascii output
            $dump .= sprintf("%04$x  %-49s  |%s|", $offset, $hexi, $ascii);

            // Reset vars
            $hexi   = $ascii = '';
            $offset += 16;
            $j      = 0;

            // Add newline
            if ($i !== $len - 1) {
                $dump .= "\n";
            }
        }
    }

    // Finish dump
    $dump .= $htmloutput === true ?
                '</pre>' :
                '';
    $dump .= "\n";

    // Output method
    if ($return === false) {
        echo $dump;
    } else {
        return $dump;
    }
}

?>

Src: http://aidanlister.com/repos/v/function.hexdump.php