Here is how I tested these (correctly, I hope): 
#!/usr/bin/perl -w
use strict;
use Benchmark qw( timethese );

use vars qw( %hash );
@hash{ 'A' .. 'Z', 'a' .. 'z' } = (1) x 52; 

timethese 100000, {
        'defined' => sub {
                if (defined $hash{X}) { };
        },
        'exists' => sub {
                if (exists $hash{X}) { };
        },
        'as is' => sub {
                if ($hash{X}) { };
        },
};

[download]


the results: 

Benchmark: timing 100000 iterations of as is, defined, exists...
     as is:  1 wallclock secs ( 0.16 usr +  0.00 sys =  0.16 CPU)
            (warning: too few iterations for a reliable count)
   defined:  0 wallclock secs ( 0.16 usr +  0.00 sys =  0.16 CPU)
            (warning: too few iterations for a reliable count)
    exists:  0 wallclock secs ( 0.16 usr +  0.00 sys =  0.16 CPU)
            (warning: too few iterations for a reliable count)

In reply to Re^2: Hashing it out: defined? exists? by eff_i_g
in thread Hashing it out: defined? exists? by eff_i_g

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