my $ismember = exists $hash{string};

##</code><code>##

my %hash = map { $_ => $_ } @array;
print($hash{string1}, "\n");
print($hash{string2}, "\n");
print($hash{string3}, "\n");

##</code><code>##

use List::Util qw( first );
my $idx = first { $array[$_] eq "string" } 0..$#array;

##</code><code>##

sub ismember {
   my ($array, $search) = @_;
   for my $i (0..$#$array) {
      return $i if $array->[$i] eq $search;
   }
   return ();
}

my $idx = ismember(\@array, "string");