Where did keyword2 go? Perhaps this was a design decision. If not, adding the line @{$hash{$currentkey}} = (); into the if( $inkey == 0 ) block does the trick.

P.S.: In order to make Data::Dumper print very nice output, pass it a hash reference, as in Dumper(\%hash). Then the output is as follows:

$VAR1 = {
          'mykeyword3' => [
                            'baz3',
                            'foo3',
                            'bar3'
                          ],
          'mykeyword2' => [],
          'mykeyword1' => [
                            'foo1',
                            'bar1'
                          ],
          'mykeyword4' => [
                            'baz4'
                          ]
        };
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P.P.S.: Can some enlightened monk tell me the preferred way to "touch" an array (reference). That is, if I only want to clear an array if it doesn't already exist (see my @{$hash{$currentkey}} = (); addition above). The snippet push @{$hash{$currentkey}}; works but produces a Useless use of push with no values warning.

P.P.S.: Can some enlightened monk tell me the preferred way to "touch" an array (reference). That is, if I only want to clear an array if it doesn't already exist (see my @{$hash{$currentkey}} = (); addition above). The snippet push @{$hash{$currentkey}}; works but produces a Useless use of push with no values warning.

I typically use:

$hash{$currentkey} ||= [];

Which will set it to an empty array ref, if it isn't already a 'true' value, and undefined isn't true ... of course, there's lots of other not true values, as well (empty string, 0, etc.)

@{$hash{$currentkey}} is an array so you can truncate the array just as you would any other array. You don't need to use push. Both of these will do the trick

@{$hash{$currentkey}} = ();
$#{$hash{$currentkey}} = -1;
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Lupey

I would like to create the array if it doesn't exist and not do anything otherwise. This is similar to the touch command in Unix-like environments. The command push @{$ref}; does exactly that: it pushes nothing onto the array, which creates it if necessary but doesn't change it if it exists.