<?php
$pattern=<<<PTN
#<a id="dnn_ctr[0-9]+_EditHTML_cmdUpdate" class="CommandButton" href="javascript:__doPostBack\('dnn\$ctr[0-9]+\$EditHTML\$cmdUpdate',''\)" style="display:inline-block;border-style:None;">Update</a>#
PTN;
$string = <<<PTN
     <a id="dnn_ctr6450_EditHTML_cmdUpdate" class="CommandButton" href="javascript:__doPostBack\('dnn\$ctr6450\$EditHTML\$cmdUpdate',''\)" style="display:inline-block;border-style:None;">Update</a>&nbsp;
PTN;
$string = str_replace("'", "\'", $string);
$string = str_replace("\"", "\\\"", $string);
echo "<BR/>Pattern: " . htmlspecialchars($pattern);
echo "<BR/><BR/>Data: " . htmlspecialchars($string);
echo "<BR/><BR/>Matched? " . preg_match($pattern, $string);

/*
 Output:
Pattern: #<a id="dnn_ctr[0-9]+_EditHTML_cmdUpdate" class="CommandButton" href="javascript:__doPostBack\('dnn$ctr[0-9]+$EditHTML$cmdUpdate',''\)" style="display:inline-block;border-style:None;">Update</a>#

Data: <a id=\"dnn_ctr6450_EditHTML_cmdUpdate\" class=\"CommandButton\" href=\"javascript:__doPostBack\(\'dnn$ctr6450$EditHTML$cmdUpdate\',\'\'\)\" style=\"display:inline-block;border-style:None;\">Update</a>&nbsp;

Matched? 0
*/
?>