Perl Cookbook (2024)

You want to remove an entry from a hash so that it doesn’t showup with keys, values, oreach. If you were using a hash to associatesalaries with employees, and an employee resigned, you’d wantto remove their entry from the hash.

Use the delete function:

# remove $KEY and its value from %HASHdelete($HASH{$KEY});

Sometimes people mistakenly try to use undef toremove an entry from a hash. undef $hash{$key} and $hash{$key} = undef both make%hash have an entry with key$key and value undef.

The delete function is the only way to remove aspecific entry from a hash. Once you’ve deleted a key, it nolonger shows up in a keys list or aneach iteration, and exists willreturn false for that key.

This demonstrates the difference between undef anddelete:

# %food_color as per Introductionsub print_foods { my @foods = keys %food_color; my $food; print "Keys: @foods\n"; print "Values: "; foreach $food (@foods) { my $color = $food_color{$food}; if (defined $color) { print "$color "; } else { print "(undef) "; } } print "\n";}print "Initially:\n";print_foods();print "\nWith Banana undef\n";undef $food_color{"Banana"};print_foods();print "\nWith Banana deleted\n";delete $food_color{"Banana"};print_foods(); Initially: Keys: Banana Apple Carrot Lemon Values: yellow red orange yellow  With Banana undef Keys: Banana Apple Carrot Lemon Values: (undef) red orange yellow  With Banana deleted Keys: Apple Carrot Lemon Values: red orange yellow ...