I want to check if a value is inside a set of predefined values.

I would use grep.

#!/usr/bin/perl -w
use strict;

my @fruits = qw(banana plum apple strawberry pea);

if ( grep {/apple/}@fruits ) #perhaps /^apple$/ 
{
   print "apple found!\n";
}
else
{
   print "apple not fouund\n";
}

__END__
apple found!
[download]

There are other ways see: List::Util