<?php
$string = 'categoryparameterusedpricing_15';
// look for a match
preg_match("/[categoryparameterusedpricing_/\d]/", $string, $matches);
echo $matches[0];
Warning: preg_match(): Unknown modifier '\' in /in/iLINB on line 6
Warning: Trying to access array offset on null in /in/iLINB on line 7
Output for 8.3.5
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
Warning: preg_match(): Unknown modifier '\' in /in/iLINB on line 6
Warning: Trying to access array offset on null in /in/iLINB on line 7