#!/usr/bin/perl

#<--------------------------# Where are 'use strict;', 'use warnings;'?
open $fb, "myfilename.txt"; # What if the file is missing?

while ($line=<$fb>)         # What if you forgot you're using $line elsewhere? 
{
		#<------------------# Perl ignores whitespace but why be messy?
	chomp($line);
	if ($.=<>){             # `=` is not a comparison operator!
			print length "$line";
                # ^---------# ... and then a newline character?
			}               # Odd indentation makes it hard to tell what this matches.
	#<----------------------# Perl ignores whitespace but why be messy?
}