You're better off using a regex for this.  In particular, a m//g (global) match in scalar context:

my $char = '-';
    
while (<DATA>) {
    print;

    while (/($char+)/g) {
 
        my $to = pos();
        my $from = $to - length($1) + 1;
        
        print "  Found $char at $from to $to\n";
    }
}

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

Output:

A-----B
  Found - at 2 to 6
A----C---B
  Found - at 2 to 5
  Found - at 7 to 9
[download]

See m//g and pos.