In Regexes§

See primary documentation in context for Named captures

Instead of numbering captures, you can also give them names. The generic, and slightly verbose, way of naming captures is like this:

if 'abc' ~~ / $<myname> = [ \w+ ] / {
    say ~$<myname>      # OUTPUT: «abc␤» 
}

The square brackets in the above example, which don't usually capture, will now capture its grouping with the given name.

The access to the named capture, $<myname>, is a shorthand for indexing the match object as a hash, in other words: $/{ 'myname' } or $/<myname>.

We can also use parentheses in the above example, but they will work exactly the same as square brackets. The captured group will only be accessible by its name as a key from the match object and not from its position in the list with $/[0] or $0.

Named captures can also be nested using regular capture group syntax:

if 'abc-abc-abc' ~~ / $<string>=( [ $<part>=[abc] ]* % '-' ) / {
    say ~$<string>;          # OUTPUT: «abc-abc-abc␤» 
    say ~$<string><part>;    # OUTPUT: «abc abc abc␤» 
    say ~$<string><part>[0]; # OUTPUT: «abc␤» 
}

Coercing the match object to a hash gives you easy programmatic access to all named captures:

if 'count=23' ~~ / $<variable>=\w+ '=' $<value>=\w+ / {
    my %h = $/.hash;
    say %h.keys.sort.join: ', ';        # OUTPUT: «value, variable␤» 
    say %h.values.sort.join: ', ';      # OUTPUT: «23, count␤» 
    for %h.kv -> $k, $v {
        say "Found value '$v' with key '$k'";
        # outputs two lines: 
        #   Found value 'count' with key 'variable' 
        #   Found value '23' with key 'value' 
    }
}

A more convenient way to get named captures is by using named regex as discussed in the Subrules section.