preg_replace_callback function name with parameter in string - php

Question

I am trying to use preg_replace_callback() to call any function with its parameter(s) embedded in a string.
$string = "some text ucfirst('asd')";
$pattern = "~ucfirst([a-z]+)\(\)~";
$string = preg_replace_callback($pattern, "ucasef", $string);
echo $string; // some text Asd
I need some help with the pattern but also with how to use it to accomplish the example output.

Answer 1

This is how you may use it, I've added some comments to clarify the code:
$input = "some text ucfirst('name') and strtoupper (\"shout\" ). Maybe also make it strtolower( 'LOWER') or do('nothing').";
$pattern = '~
(\w+) # Match the function name and put it in group 1
\s*\(\s* # Some optional whitespaces around (
("|\') # Match either a double or single quote and put it in group 2
(.*?) # Match anything, ungreedy until ...
\2 # Match what was matched in group 2
\s*\) # Some optional whitespaces before )
~xs'; # XS modifiers, x to make this fancy formatting/commenting and s to match newlines with the dot "."
$output = preg_replace_callback($pattern, function($v){
$allowed = array('strtolower', 'strtoupper', 'ucfirst', 'ucwords'); // Allowed functions
if(in_array(strtolower($v[1]), $allowed)){ // Check if the function used is allowed
return call_user_func($v[1], $v[3]); // Use it
}else{
return $v[0]; // return the original value, you might use something else
}
}, $input);
echo $output;
Output: some text Name and SHOUT. Maybe also make it lower or do('nothing').