my $string = "1-2, 3-4, 5-6";


#strip anything but the last digit,
$string =~ s/^.*(\d)$/$1/;
# string now holds only the last digit, rest should be removed
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or

my $last_digit = '';
if ($string =~ /(\d)$/) {
    $last_digit = $1;
}
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or

my $last_digit = '';
if ($string =~ /(\d){1}$/) {
    $last_digit = $1;
}
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In the last example you may replace {1} if you want any other number of digits from the end of the string

Hope this helps
RL