Question

I have the folowing code:

<?php
$subject = "Replace ? question mark in brackets [? with ? incremental ??]? digits";
echo incremental_replace($subject);
// i want the folowing: 
// Replace ? question mark in brackets [1 with 2 incremental 34]? digits

I want all the ? in the brackets to be replaced. Also, the number and position of ? can change.

How do i do that with php ? I think this can be done with preg_replace, but i don’t know how.

Answer 1

if brackets are not nested, then the following would be enough

echo preg_replace('~\?(?=[^\[\]]*\])~e', '++$n', $subject);

otherwise use a parser:

$subject = "Replace ? question mark in [nested ? brackets] [? with ? [incremental ? [?]] ??]? digits";
$result = '';

$bc = $n = 0;
foreach(str_split($subject) as $c) {
    if($c == '[') $bc++;
    if($c == ']') $bc--;
    if($c == '?' && $bc) $c = ++$n;
    $result .= $c;
}

echo $result;

A regular expression for nested brackets is possible but will be too long and messed up.

---

Note by OP: If the replacements are not incremental digits but an array, you can do the folowing:

$n = 0;
$rep = array('foo', 'bar', 'baz', 'qux', 'quux');
echo preg_replace('~\?(?=[^\[\]]*\])~e', '$rep[$n++]', $subject);