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 );