The following (inefficiently) deletes all the values of %HASH:

    foreach $key (keys %HASH) { delete $HASH{$key}; }
    foreach $index (0 .. $#ARRAY) { delete $ARRAY[$index]; }

And so do these:

    delete @HASH{keys %HASH};
    delete @ARRAY[0 .. $#ARRAY];

But both of these are slower than just assigning the empty list or undefining %HASH or @ARRAY:

    %HASH = ();         # completely empty %HASH
    undef %HASH;        # forget %HASH ever existed

    @ARRAY = ();        # completely empty @ARRAY
    undef @ARRAY;       # forget @ARRAY ever existed