PHP: str_replace that only acts on the first match?

Question

I want a version of strreplace() that only replaces the first match in the target string. Is there an easy solution to this, or do I need a hacky solution?

Answer 1

Can be done with preg_replace:

<?
$str = 'abcdef abcdef abcdef';
// pattern, replacement, string, limit
echo preg_replace('/abc/', '123', $str, 1); // 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).

Answer 2

The easiest way would be to use regular expression.

The other way is to find the position of the string with strpos() and then an substr_replace()

But i would really go for the RegExp.

Answer 3

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($replace));
}

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

Answer 4

Unfortunately I don't know of any PHP funciton which can do this. You can roll your own fairly easily like this:

function replace_first($find, $replace, $subject) {
    // stolen from the comments at PHP.net/str_replace
    return implode($replace, explode($find, $subject, 1));
}

Answer 5

The answers by 'zombat' and 'too much php' are unfortunately not correct. This is a revision to the answer zombat posted (as I don't have enough reputation to post a comment):

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

Note the strlen($needle), instead of strlen($replace). Zombat's example will only work correctly if needle and replace are the same length.

Here's the same functionality in a function with the same signature as PHP's own str_replace:

function str_replace_first($search, $replace, $subject) {
    $pos = strpos($subject, $search);
    if ($pos !== false) {
        $subject = substr_replace($subject, $replace, $pos, strlen($search));
    }
    return $subject;
}

This is the revised answer of 'too much php':

implode($replace, explode($search, $subject, 2));

Note the 2 at the end instead of 1. Or in function format:

function str_replace_first($search, $replace, $subject) {
    return implode($replace, explode($search, $subject, 2));
}

I timed the two functions and the first one is twice as fast when no match is found. They are the same speed when a match is found.