PHP preg_replace - finding the replacement from an array using the match as the key

Question

I have a string which can contain multiple matches (any word surrounded by percentage marks) and an array of replacements - they key of each replacement being the match of the regex. Some code will probably explain that better...

$str = "PHP %foo% my %bar% in!";
$rep = array(
  'foo' => 'does',
  'bar' => 'head'
);

The desired result being:

$str = "PHP does my head in!"

I have tried the following, none of which work:

$res = preg_replace('/\%([a-z_]+)\%/', $rep[$1], $str);
$res = preg_replace('/\%([a-z_]+)\%/', $rep['$1'], $str);
$res = preg_replace('/\%([a-z_]+)\%/', $rep[\1], $str);
$res = preg_replace('/\%([a-z_]+)\%/', $rep['\1'], $str);

Thus I turn to Stack Overflow for help. Any takers?

Answer 1

echo preg_replace('/%([a-z_]+)%/e', '$rep["$1"]', $str);

gives:

PHP does my head in!

See the docs for the modifier 'e'.

Answer 2

You could use the eval modifier...

$res = preg_replace('/\%([a-z_]+)\%/e', "\$rep['$1']", $str);

Answer 3

Just to provide an alternative to preg_replace():

$str = "PHP %foo% my %bar% in!";
$rep = array(
  'foo' => 'does',
  'bar' => 'head'
);


function maskit($val) {
    return '%'.$val.'%';
}

$result = str_replace(array_map('maskit',array_keys($rep)),array_values($rep),$str);
echo $result;