my @alternatives = qw(ABA SCO ACC PHC GHF);

my $target = 'ABA';

if (grep {$target eq $_} @alternatives) {

    print "$target is in (@alternatives)\n";

}
else {

    print "$target is not in (@alternatives)\n";

}
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The meat is this:  if (grep {$target eq $_} @alternatives) ....

Here's how it works. First, grep will iterate over the elements in @alternatives, and compare each element to your $target value. In scalar context (provided by the if(CONDITION) construct), grep returns the number of matches. In Perl, any numeric value that is not zero is true in a Boolean sense. So getting a match on one of the elements will make the condition true.

You can set up an "all" relationship (instead of "any") like this:

Here we're asserting that every element in @alternatives must match $target.