The defined-or operator is just //. $lvalue //= "value"; actually means $lvalue = "value" unless defined $lvalue;. This means that you actually write "Key '$inData' doesn't exist.\n" in the hash : 

use Data::Dumper;

my %words = ( 'hello' => 'world' );

print 'type a word: ';
chomp( my $inData = <> );
print $words{$inData} //= "Key '$inData' doesn't exist.\n";

print Dumper \%words;

[download]
type a word: Bonjour
Key 'Bonjour' doesn't exist.
$VAR1 = {
          'hello' => 'world',
          'Bonjour' => 'Key \'Bonjour\' doesn\'t exist.
'
        };

[download]
You meant print $words{$inData} // "Key '$inData' doesn't exist.\n"; which works fine as long as undef isn't a valid value.

In reply to Re^2: Getting values from a Hash from user input by Eily
in thread Getting values from a Hash from user input by blueblue

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