If you are searching through the array multiple times, then right, this isn't the best option. If you are reusing the array to compare against, the best practice is this:

my @array = qw ( a b c d x );
my %hashcheck;
@hashcheck{@array} = ();

my $sought = 'a';
print "Found!" if exists $hashcheck{$sought};
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The reason they suggest not using grep is because it is a O(n) algorithm whereas checking for exists is O(1). When you continuously check @array to see whether or not items can be found, it would be much slower to use grep.

As for their suggestion in the case that the array is checked only once, I could go either way. Their method is actually 17% faster on a million iterations (my benchmarks, YMMV), but I find grep easier to read.

antirice    
The first rule of Perl club is - use Perl
The ith rule of Perl club is - follow rule i - 1 for i > 1