The length issue you encountering comes about because the string you input is terminated with the newline character (\n), hence its length is 5 visible characters plus the newline. If you print $str, you will see the cursor advance a line. You should be able to fix it by inserting the following line after line 7:

chomp $str;

However, it seems like you already knew that, so I can only assume you are using chomp wrong. Since you say that your string ends up with a length of 1, I'd wager your code is

$str = chomp $str; #Wrong!

chomp magically acts upon the arguments and does not require you to reassign.