Perl beginner: IF syntax for empty input

Question

I have typed a little program to refresh my Perl knowledge, especially the IF and Else-Case I was interested in. How do I make Perl recognize that the input was empty? I checked the input with "==" and also with "eq" but my program always says "You have typed nothing!".

#!/usr/bin/perl

# input line
$input_line = "";

# terminal input
print "Input:";
$input_line = <STDIN>;

# input verification
print "Your input was: ", "$input_line";
print "\n";

# decider terminal input
if ($input_line ==  "" or $input_line eq "")
   { print "You have typed nothing!";
     print "\n"; }
     
   else
        { print "Typing nothing is bad!";
          print "\n"; }

And the output if I type "Hello" is:

Input:Hello
Your input was: Hello

You have typed nothing!

If I type Hello, then there is input.

If I type nothing, then the output should write "You have typed nothing!", and the Else-Case should also appear.

Answer 1

Always add use warnings; to your code to get more information as to why it does not work:

Argument "" isn't numeric in numeric eq (==) at ... line ..., line 1.

One approach is to check the length of the string input. It is also a good practice to chomp the input to remove any newline character.

use warnings;
use strict;

# input line
my $input_line = "";

# terminal input
print "Input:";
$input_line = <STDIN>;
chomp $input_line;

# input verification
print "Your input was: ", "$input_line";
print "\n";

# decider terminal input
if (length($input_line) == 0) {
    print "You have typed nothing!";
    print "\n";
}

It is also good practice to add use strict;. In this case you need to declare variables with my.

Since you are new to Perl, refer to the Basic debugging checklist