preg_replace /e and array

Question

why this code does not work ?

$mx['foo'] = "vvv";
$string = "foo is foobar, baz is widgets";
echo preg_replace("/(foo)/ei",  "$mx[('\\1')]",  $string );

the output must like this

vvv is vvvbar, baz is widgets

Answer 1

Because you are using double quotes in preg_replace, PHP tries to use your$mx value directly, which produces then error...

Simply escape the $mx, and then it will work:

echo preg_replace("/(foo)/ei",  "\$mx[('\\1')]",  $string );

Or you can do the same by using single quotes:

echo preg_replace("/(foo)/ei",  '$mx[(\'\\1\')]',  $string );

Answer 2

Your preg_replace uses double quotes, which are interpreted by PHP. It does not look like you need such a complex setup, since this is a simple string replacement, as far as i can see. A simpler solution would be:

$string = str_replace('foo', 'vvv', $string);

You could use your array, too:

$replacements = array(
    'foo' => 'vvv'
);
foreach ($replacements as $key => $replacement) {
    $string = str_replace($key, $replacement, $string);
}

This would replace all keys in the given array with the associated values.