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delete

Perl 5 version 26.0 documentation
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delete

Perl functions A-Z | Perl functions by category | The 'perlfunc' manpage
  • delete EXPR

    Given an expression that specifies an element or slice of a hash, delete deletes the specified elements from that hash so that exists on that element no longer returns true. Setting a hash element to the undefined value does not remove its key, but deleting it does; see exists.

    In list context, returns the value or values deleted, or the last such element in scalar context. The return list's length always matches that of the argument list: deleting non-existent elements returns the undefined value in their corresponding positions.

    delete may also be used on arrays and array slices, but its behavior is less straightforward. Although exists will return false for deleted entries, deleting array elements never changes indices of existing values; use shift or splice for that. However, if any deleted elements fall at the end of an array, the array's size shrinks to the position of the highest element that still tests true for exists, or to 0 if none do. In other words, an array won't have trailing nonexistent elements after a delete.

    WARNING: Calling delete on array values is strongly discouraged. The notion of deleting or checking the existence of Perl array elements is not conceptually coherent, and can lead to surprising behavior.

    Deleting from %ENV modifies the environment. Deleting from a hash tied to a DBM file deletes the entry from the DBM file. Deleting from a tied hash or array may not necessarily return anything; it depends on the implementation of the tied package's DELETE method, which may do whatever it pleases.

    The delete local EXPR construct localizes the deletion to the current block at run time. Until the block exits, elements locally deleted temporarily no longer exist. See Localized deletion of elements of composite types in perlsub.

    1.     my %hash = (foo => 11, bar => 22, baz => 33);
    2.     my $scalar = delete $hash{foo};         # $scalar is 11
    3.     $scalar = delete @hash{qw(foo bar)}; # $scalar is 22
    4.     my @array  = delete @hash{qw(foo baz)}; # @array  is (undef,33)

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

    1.     foreach my $key (keys %HASH) {
    2.         delete $HASH{$key};
    3.     }
    5.     foreach my $index (0 .. $#ARRAY) {
    6.         delete $ARRAY[$index];
    7.     }

    And so do these:

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

    But both are slower than assigning the empty list or undefining %HASH or @ARRAY, which is the customary way to empty out an aggregate:

    1.     %HASH = ();     # completely empty %HASH
    2.     undef %HASH;    # forget %HASH ever existed
    4.     @ARRAY = ();    # completely empty @ARRAY
    5.     undef @ARRAY;   # forget @ARRAY ever existed

    The EXPR can be arbitrarily complicated provided its final operation is an element or slice of an aggregate:

    1.     delete $ref->[$x][$y]{$key};
    2.     delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};
    4.     delete $ref->[$x][$y][$index];
    5.     delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];