php - preg_replace all occurrences in string withing defined delimeters -

i trying replace occurrences of "a" "b" inside string. problem need replace letters inside brackets:

asd asd asd [asd asd asd] asd asd asd

for have code:

$what = '/(?<=\[)a(?=.*?\])/s'; $with = 'b'; $where = 'asd asd asd [asd asd asd] asd asd asd'; 

but replaces first "a", , getting result:

asd asd asd [bsd asd asd] asd asd asd

i realy need done 1 preg_replace call.

you cannot single preg_replace call because lookbehind need "there opening square bracket somewhere before match" , impossible since lookbehind patterns must have fixed length.

why absolutely need in 1 call anyway? doable pretty preg_replace_callback, match groups of content inside square brackets , use preg_replace on match each time (or simple str_replace if going replace "a" "b").

example:

$what = '/\[([^]]*)\]/'; $where = 'asd asd asd [asd asd asd] asd asd asd';  echo preg_replace_callback(     $what,      function($match) {         return '['.str_replace('a', 'b', $match[1]).']';     },     $where);