- var_dump: documentation ( source)
- strpos: documentation ( source)
- print_r: documentation ( source)
- preg_match_all: documentation ( source)
<?php
$etag = '"123-456\"789"';
$regex = '~(?:^|[\h,]+)(?:W/)?(")?(?(1)((?:[^"\\\\]|\\\\.)*(*MARK:Q))(?:"|\\\\|$)|([^,]*(*MARK:T)))~';
\preg_match_all($regex, $etag, $matches, \PREG_SET_ORDER);
print_r($matches);
var_dump(strpos('123\'123', '\\'));