format string %key% => array('key'=>'bla');

string_format.php

<?php
/**
 * @param string $string
 * @param array $replacements
 * @param string $begin
 * 
 * @return string
 * 
 * @example "string_format_example.php"
 */
function string_format($string, array $replacements = array(), $begin = '%'){
	$reverse_chars = array('(' => ')', '[' => ']', '{' => '}', '<' => '>');
	$end = strtr(strrev($begin), array_merge($reverse_chars, array_flip($reverse_chars)));
	$replacements = array_combine(array_map(function ($key) use ($begin, $end) {
		return $begin . $key . $end;
	}, array_keys($replacements)), $replacements);
	return strtr($string, $replacements);
}

string_format_example.php

<?php

// output: Ruben said hello!
echo string_format("%person% said %greeting%!", array(
  'person'	=>'Ruben',
  'greeting	=>'hello'
));