Replace substrings with an incremented counter value

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 follow

Answer 1

I prefer to use preg_replace_callback() for this task . It is a more direct solution than making iterated single preg_replace() calls which restart from the beginning of the string each time (checking text that has already been replaced).

• ^ means the start of a line because of the m pattern modifier.
• \K means restart the full string match. This effectively prevents the literal > from being replaced and so only the literal string num is replaced.
• the static counter declaration will only set $counter to 0 on the first visit.
• the custom function does not need to receive the matched substring because the entire full string match is to be replaced.

Code: (Demo)

$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
     );