use strict; use warnings; use feature 'say';

# This section creates a temporary file for testing
my $file = "/tmp/$0.txt";
open TMP, '>', $file or die "Died: $!";
print TMP for (<DATA>);
close TMP;
#-------------------------------------------------#

print 'Which line would you like to measure? ';
chomp( my $wanted = <STDIN> );
die 'Died: wanted line number required' if not $wanted;

open my $FH, '<', $file or die "Died: $!";

while ( my $line = <$FH> ) {
    chomp $line;
    if ( $. == $wanted ) {
        say "The length of line $wanted ('$line') is " . length $line;
        last;
    }
    say "Reached end of file before line $wanted" if eof;
}

# remove the test file
unlink $file;

__DATA__
heaven
heavenly
heavenns
abc
heavenns
heavennly