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my %hash = qw(
       $bar => 1
...
       $boo => 1
);
print "yep!\n" if exists $hash{$foo};

Regex Solution
timethis 100000: 18 wallclock secs ( 0.41 usr +  0.05 sys =  0.45 CPU)

Hash Solution
timethis 100000:  1 wallclock secs ( 1.58 usr +  0.00 sys =  1.58 CPU)