Question

preg_replace("/\[b\](.*)\[\/b\]/Usi", "<strong>$1</strong>", "Some text here... [b][b]Hello, [b]PHP![/b][/b][/b] ... [b]and here[/b]");

returns

Some text here... <strong>[b]Hello, [b]PHP!</strong>[/b][/b] ... <strong>and here</strong>

But i need to replace all [b]…[/b] tags. Why this doesn’t happen in my case?

Answer 1

The reason it doesn’t work: You catch the first [b], then move on to the next [/b], and leave anything in between unchanged. Ie, you change the outer [b] tags, but not the ones nested inside.

Your comment to @meza suggests you want to replace the pseudo tags in pairs, or else leave them untouched. The best way to do this is to use multiple passes, like this

$markup = "Some text here... [b][b]Hello, [b]PHP![/b][/b][/b] ... [b]and here[/b]";
$count = 0;
do {
    $markup = preg_replace("/\[b\](.*?)\[\/b\]/usi", "<strong>$1</strong>", $markup, -1, $count );
} while ( $count > 0 );

print $markup;

I’m not even sure if you can do it in a one-line regex, but even if you could, it would be rather complex and therefore hard to maintain.