Here's a marginally more clever version of your solution, which relies on the placeholder capabilities of a /g search. I mention it because I think it's a tiny bit more readable than the version you wrote. But ... you know ... personal preference and all that.

use strict;
use warnings;

my $test_string = "3 xyz";

# Start a global search
# It looks like the expected pattern includes a space. Let's put it he
+re.
if ( $test_string =~ m/^(\d+) /g ) {
    my $length = $1;

    # Pick up the search where our first match left off.
    if ( $test_string =~ m/\G(.{$length})/ ) {
        my $result = $1;
        # Do stuff with $result ...
    }
}

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In reply to Re^2: Backref in a regex quantifier by webfiend
in thread Backref in a regex quantifier by Anonymous Monk

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