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#1: FAQ 4.44 How do I test whether two arrays or hashes are equal?

Posted on 2008-04-19 03:03:02 by PerlFAQ Server

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at .

------------------------------------------------------------ --------

4.44: How do I test whether two arrays or hashes are equal?

The following code works for single-level arrays. It uses a stringwise
comparison, and does not distinguish defined versus undefined empty
strings. Modify if you have other needs.

$are_equal = compare_arrays(\@frogs, \@toads);

sub compare_arrays {
my ($first, $second) = @_;
no warnings; # silence spurious -w undef complaints
return 0 unless @$first == @$second;
for (my $i = 0; $i < @$first; $i++) {
return 0 if $first->[$i] ne $second->[$i];
return 1;

For multilevel structures, you may wish to use an approach more like
this one. It uses the CPAN module "FreezeThaw":

use FreezeThaw qw(cmpStr);
@a = @b = ( "this", "that", [ "more", "stuff" ] );

printf "a and b contain %s arrays\n",
cmpStr(\@a, \@b) == 0
? "the same"
: "different";

This approach also works for comparing hashes. Here we'll demonstrate
two different answers:

use FreezeThaw qw(cmpStr cmpStrHard);

%a = %b = ( "this" => "that", "extra" => [ "more", "stuff" ] );
$a{EXTRA} = \%b;
$b{EXTRA} = \%a;

printf "a and b contain %s hashes\n",
cmpStr(\%a, \%b) == 0 ? "the same" : "different";

printf "a and b contain %s hashes\n",
cmpStrHard(\%a, \%b) == 0 ? "the same" : "different";

The first reports that both those the hashes contain the same data,
while the second reports that they do not. Which you prefer is left as
an exercise to the reader.

------------------------------------------------------------ --------

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