I tend to use hashes if the set is larger, but I stay with grep if not and the test is not repeated much:

#!/usr/bin/perl
use warnings;
use strict;

my @values = qw/banana plum apple strawberry pea/;
my $var = 'apple';
my %hash;
undef @hash{@values};
print exists $hash{$var} ? "yes\n" : "no\n";

print +(grep $_ eq $var, @values) ? "yes\n" : "no\n";
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