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11.3. Taking References to Hashes
11.3.1. Problem
You need to manipulate a hash by reference.
This might be because it was passed into a function that way or
because it's part of a larger data
structure.
11.3.2. Solution
To get a hash reference:$href = = { "key1" => "value1", "key2" => "value2", ... };
$anon_hash_copy = { %hash };
To dereference a hash reference:%hash = %$href;
$value = $href->{$key};
@slice = @$href{$key1, $key2, $key3}; # note: no arrow!
@keys = keys %$href;
To check whether something is a hash reference:if (ref($someref) ne "HASH") {
die "Expected a hash reference, not $someref\n";
}
11.3.3. Discussion
This example prints out all keys and values from two predefined
hashes:foreach $href ( \%ENV, \%INC ) { # OR: for $href ( \(%ENV,%INC) ) {
foreach $key ( keys %$href ) {
print "$key => $href->{$key}\n";
}
}
Access slices of hashes by reference as you'd access slices of arrays
by reference. For example:@values = @$hash_ref{"key1", "key2", "key3"};
for $val (@$hash_ref{"key1", "key2", "key3"}) {
$val += 7; # add 7 to each value in hash slice
}
11.3.4. See Also
The Introductionin Chapter 5; Chapter 8 of
Programming Perl;
perlref(1); Recipe 11.9
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| 11.2. Making Hashes of Arrays |  | 11.4. Taking References to Functions |
Copyright © 2003 O'Reilly & Associates. All rights reserved.
