Using str_replace so that it only acts on the first match?


I want a version of str_replace() that only replaces the first occurrence of $search in the $subject. Is there an easy solution to this, or do I need a hacky solution?

5/7/2014 3:51:59 PM

Accepted Answer

Can be done with preg_replace:

function str_replace_first($from, $to, $content)
    $from = '/'.preg_quote($from, '/').'/';

    return preg_replace($from, $to, $content, 1);

echo str_replace_first('abc', '123', 'abcdef abcdef abcdef'); 
// outputs '123def abcdef abcdef'

The magic is in the optional fourth parameter [Limit]. From the documentation:

[Limit] - The maximum possible replacements for each pattern in each subject string. Defaults to -1 (no limit).

Though, see zombat's answer for a more efficient method (roughly, 3-4x faster).

2/22/2018 5:16:53 PM

There's no version of it, but the solution isn't hacky at all.

$pos = strpos($haystack, $needle);
if ($pos !== false) {
    $newstring = substr_replace($haystack, $replace, $pos, strlen($needle));

Pretty easy, and saves the performance penalty of regular expressions.

Bonus: If you want to replace last occurrence, just use strrpos in place of strpos.

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