- preg_replace_callback: documentation ( source)
<?php
$text = <<<TEXT
>num, blah, blah, blah
ATCGACTGAATCGA
>num, blah, blah, blah
ATCGATCGATCGATCG
>num, blah, blah, blah
ATCGATCGATCGATCG
TEXT;
echo preg_replace_callback(
"~^>\Knum~m",
function () {
static $counter = 0;
return ++$counter;
},
$text
);