All caveats aside for the many cases where this will cause false positives, I'd write it with a regex for expressiveness:

my @array = qw ( a b c d x );
my $sought = 'a';
print 'Found!' if "@array" =~ /\Q$sought/;
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While it is very slightly less efficient as it needs to be compiled, the regex engine will see it is dealing with a fixed string and use shortcuts rather than generic pattern matching, so that will only matter in a tight loop processing a lot of data. However I find it reads a lot more naturally.

Makeshifts last the longest.