Is it possible to have logic in PHP's preg_replace function's replace parameter?

Question

Here is some PHP that I want to replace with something else.

Ks. <?kys(1959,"kysymys 1959")?>.
Ks. <?kys(1959)?>.

I have this regular expression, which finds both and works fine:

<\?kys\((\d+)(,"([\s\S]+)")?\)\?>

I tested (and designed) it with Regex101.com: https://regex101.com/r/kcDpN3/1

So there will at least be match $1. But there can also be matches $2 and $3. Is it possible to have preg_replace replace the matches with the following logic: if $3, use $3; else use $1?

No, because it will just concatenate both matches, which isn't what I want. I want either or. — Simon Josef Kok
– Simon Josef Kok, Commented Sep 30, 2020 at 11:18

Wiktor Stribiżew · Accepted Answer · 2020-09-30 11:27:53Z

2

You may use preg_replace_callback.

See the PHP demo:

$str = 'Ks. <?kys(1959,"kysymys 1959")?>.
Ks. <?kys(1959)?>.';
$re = '/<\?kys\((\d+)(?:,"([^"]+)")?\)\?>/';

echo preg_replace_callback($re, function($m) {
    return empty($m[2]) ? $m[1] : $m[2];
}, $str);

Here, the second group in your pattern was turned into non-capturing one (?: added after () and now there are only two groups to handle.

The $m is the whole match object, and if Group 2 is empty, the replacement is Group 1 value ($m[1]). Else, it is Group 2 value, $m[2].

Note I also replaced [\s\S]+ with [^"]+ to make it match till the first ". Replace with .*? and add /s flag if there can be " inside Group 2.

answered Sep 30, 2020 at 11:27

Wiktor Stribiżew

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