How do extract a substring using regular expressions in Chapel? - regex

Question

I know that Chapel has the Regexp Library but I don't understand how to use capturing groups. Could someone provide an example?
var template = "/home/user/:ID/details";
var uid = someKindaExtractyThing("/home/user/17/details");
writeln("So YOU are user ", uid, ", huh?")
> So YOU are user 17, huh?
This is my target.

Answer 1

The question already linked to the documentation so all that's really left to do is to show a code example.
use Regexp;
var input = "/home/user/17/details";
var capture:string;
var r = compile("""/home/user/(\w+)/details""");
var match = r.match(input, capture);
if match.matched then
writeln(capture);
else
writeln("not a match!");
The """ business will only work with master now or Chapel 1.17 or newer (otherwise you'd have to '\'-escape the '\' in a regular "string"). The Regexp module documentation has lots more details about what you can put in a regexp.
If you had multiple capture groups, you'd use more arguments to search to get them. search looks for a pattern within a string but match insists that the entire string match the pattern.
Here is an example with 2 capture groups:
use Regexp;
var input = "/home/user/17/details";
var part1:string;
var part2:string;
var r = compile("""/home/user/(\w+)/(\w+)""");
var match = r.match(input, part1, part2);
if match.matched then
writeln( (part1,part2) );
else
writeln("not a match!");