How to get the index of the last digit in a string in Perl?

In Perl, how do you find the index of the last digit in a string?

Example: Hello123xyz index of last digit is 7

A RE to match the last digit in the string and the @- variable to get the index of the start of the match:

#!/usr/bin/env perl
use warnings;
use strict;
use feature qw/say/;

sub last_digit_index($) {
    if ($_[0] =~ /\d\D*\z/) {
        return $-[0];
    } else {
        return -1;
    }
}

say last_digit_index("Hello123xyz"); # 7

I'd probably use the pos function here. Match with /g and the Perl remembers where the match left off. The next global match on that string will start where the last match left off, so isolate this in a sub or block to avoid weird effects on subsequent matches on the same variable.

Since the position counts from 0, the next position will be one greater than the 1-based position of the final digit. You decide if you want to subtract 1 or not:

use v5.10;

say last_digit_pos('Hello123xyz');

sub last_digit_pos {
    my( $string ) = @_;
    $string =~ m/^.*\d/sg;
    return pos($string);  # 6
    }

And, if the string doesn't match, pos doesn't return a defined value.

Can also leverage List::MoreUtils::last_index

use List::MoreUtils qw(last_index);

my $last_digit_index = last_index { /[0-9]/ } split '', $string;

I find this simple: break the string into a list of characters with a typical use of split, and use a library to find the last one which is a digit, via a trivial regex.

Note that this is "expensive" as it creates a scalar for each character and runs regex multiple times. So if efficiency matters -- if this is done on an absolutely gigantic string, or many many many times on smaller strings -- then better seek other approaches, or at least benchmark before deciding.