Question

Basically what I’m looking for is the PHP version of this thread:
Find, replace, and increment at each occurence of string

I would like to replace the keyword following > at the start of rach line with an incrementing counter.

If my input is:

>num, blah, blah, blah

ATCGACTGAATCGA

>num, blah, blah, blah

ATCGATCGATCGATCG

>num, blah, blah, blah

ATCGATCGATCGATCG

I would like it to be…

>0, blah, blah, blah

ATCGACTGAATCGA

>1, blah, blah, blah

ATCGATCGATCGATCG

>2, blah, blah, blah

ATCGATCGATCGATCG

Answer 1

$str = 'a hello a some a';
$i = 0;

while (strpos($str, 'a') !== false)
{
    $str = preg_replace('/a/', $i++, $str, 1);
}

echo $str;