Replace space by underscore in pattern

replacePattern.php

<?php
/**
 * replace space by underscore in given pattern
 * written by Github user @pjdevries
 * 
 * run from command line
 * $ php unspace-anchor-names.php name-input-file > name-output-file
 * 
 */
 
function pregReplaceCallback($matches) {
    if (count($matches) > 1) {
        return str_replace($matches[1], str_replace(' ', '_', trim($matches[1])), $matches[0]);
    }

    return $matches[0];
}

if (count($argv) > 1) {
    $file = $argv[1];
} else {
    $file = 'php://stdin';
}

$fp = fopen($file, 'r');
while (($line = fgets($fp)) !== false) {
    $pattern = '/<a\s*name=\\\"([^"]*)\\\"[^>]*>/';
    echo preg_replace_callback($pattern, 'pregReplaceCallback', $line);
}