PHP将第一次出现替换为x，将第二次出现的字符串替换为y

Question

This is a tricky question here is what I am trying to do:

$str="abc def abc";

I want to replace first occurrence of abc with 123 and second occurrence of abc with 456 Now with preg_match it is possible that I replace first occurrence of abc with 123 like this

preg_replace('/abc/', '123', $str, 1);

But how to replace the second occurrence with 456 and most importantly how to do it at once and generate the required string (i.e 123 def 456).

Note: Strings are generated from external source.

Thanks Ahmar

Answer 1

You were very close:

$str = preg_replace('/abc/', '123', $str, 1); // will replace first 'abc'
$str = preg_replace('/abc/', '456', $str);    // will replace all others

The reason this will work, is because the 2nd regex's first occurence, is actually the 2nd item.
Pro: Very readable, very easy to understand and implement
Con: the string will be regexed twice (bad for large strings), options are limited

---

If this is not what you want, you can use preg_replace_callback()

$firstHasBeenFound = false;
function magicFunction($matches){
    global $firstHasBeenFound;
    print_r($matches);
    if( !$firstHasBeenFound ){
        /* do something for the first time */ ;
        $firstHasBeenFound = true; // save for next round
    }
    else{
         /* do something for the test */ ;
    }
}

$str = preg_replace_callback('/abc/', 'magicFunction', $str);

Pro: A lot more variants can be made, more control over code, only one parse of the string
Con: More difficult to read/implement

In this example I use $firstHasBeenFound, but you could use a increment to do something each 2nd, or something when you find match 7, etc