$re = '/\"channelRequestId\":\"(?<channelRequestId>[^\"]*)/';
$str = 'parameterValue={"executingDetails":{"executingxxxNumber":xx,"executingxxxxNumber":xxx},"requestorData":{"requestorIDs":{"serviceProductID":9,
"channelRequestId":"12345678-1234-xxxx-xxxx-abcdeffxxxx","variousChannelTypeCode":9},"requestData":{"referenceNumber":000000,"customerRequestTimestamp":"2017-07-24 14:37:39"}},"xxxxData":{"xxxxxxNumberxxxx":"xxx","xxxToken":"9dc2b23f-ea4a-4632-8b57-f37eaebab64c"},"debitTransactionData":{"requestAmount":1210.0,"currencyTypeCode":1}}';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php