Replace last occurrence of a string in a string

Question

You can use this function:

function str_lreplace($search, $replace, $subject)
{
    $pos = strrpos($subject, $search);

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

    return $subject;
}

Another 1-liner but without preg:

$subject = 'bourbon, scotch, beer';
$search = ',';
$replace = ', and';

echo strrev(implode(strrev($replace), explode(strrev($search), strrev($subject), 2))); //output: bourbon, scotch, and beer

$string = 'this is my world, not my world';
$find = 'world';
$replace = 'farm';
$result = preg_replace(strrev("/$find/"),strrev($replace),strrev($string),1);
echo strrev($result); //output: this is my world, not my farm

The following rather compact solution uses the PCRE positive lookahead assertion to match the last occurrence of the substring of interest, that is, an occurrence of the substring which is not followed by any other occurrences of the same substring. Thus the example replaces the last 'fox' with 'dog'.

$string = 'The quick brown fox, fox, fox jumps over the lazy fox!!!';
echo preg_replace('/(fox(?!.*fox))/', 'dog', $string);

OUTPUT: 

The quick brown fox, fox, fox jumps over the lazy dog!!!