Others have already shown you a better way to go, but here's an implementation using index just for fun:

#!/usr/bin/perl
use strict;
use warnings;

sub find_char
{
    my ($char, $string) = @_;
    my @indexes_present = ();

    my $position = 0;
    while (length($string)) {
        my $index = index($string, $char);

        if ($index != -1) {
            $position = $position + ($index+1);
            push @indexes_present, $position;
            $string = substr($string, ($index+1), (length($string)-$in
+dex));
        } else {
            last;
        }
    }
    push @indexes_present, -1;

    my ($start_of_range, $end_of_range);
    my $previous_index;
    while (my $index = shift @indexes_present) {
        if (!defined($previous_index)) {
            $start_of_range = $end_of_range = $index;
        } elsif (($previous_index+1) == $index) {
            $end_of_range = $index;
        } else {
            if ($start_of_range == $end_of_range) {
                print "Found at $start_of_range\n";
            } else {
                print "Found at $start_of_range to $end_of_range\n";
            }
            $start_of_range = $end_of_range = $index;
        }
        $previous_index = $index;
    }
}

while (<DATA>) {
    print "\n$_";
    find_char('-', $_);
}

__DATA__
A--B---C----D-E
A-B--C---D----E
---------------
[download]

Prints:

A--B---C----D-E
Found at 2 to 3
Found at 5 to 7
Found at 9 to 12
Found at 14

A-B--C---D----E
Found at 2
Found at 4 to 5
Found at 7 to 9
Found at 11 to 14

---------------
Found at 1 to 15

Press ENTER or type command to continue
[download]

So yeah. The other way is better.

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