Q:

How to convert an array to an escaped string, which I can use in a regex?

I'm querying for subnets from a database. Ultimately I'll get a bunch of subnets into an array of strings with results like:
array = ['10.1.0.1/24', '10.2.0.2/24', '192.168.0.8/16']

What's the best way to join the array above and ensure all . and / are properly escaped so I can see if a string I have matches any one of the subnets in the array?
Ideally I'd have something like: 
if (preg_match(array_as_string, $buffer, $matches)) { }

A:

First you can loop through all array values with array_map() and escape them with preg_quote(). After this you can use implode() to make them to a string, e.g.
$array = array_map(function($ip){
    return preg_quote($ip, "/");
}, $array);

if (preg_match("/\b(" . implode("|", $array) . ")\b/", $buffer, $matches)) { }

So you will end up with a regex like this:
/\b(10\.1\.0\.1\/24|10\.2\.0\.2\/24|192\.168\.0\.8\/16)\b/

