$re = '/(?:(?:A=)([^,]*))/m';
$str = '"A=1,B=2,C=3",
"A=11,B=12,C=13,D=15",
"A=5,B=4,C=9,D=10,E=13",
"A=19,B=20,C=91,D=40,E=33",
"A=77,B=27,C=37"';
preg_match_all($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