You need to do two things.

1. Iterate over the array using foreach. This avoids counting the index of the array when you aren't using it.
2. Use the exists function to test whether a value exists in the hash

The following illustrates this

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

my @array = qw (one two three four five);
my %hash = (one => 'Extra information for one',
two => 'Extra information for two');

foreach my $id (@array) {
    if (exists $hash{$id}) {
        print "ID: $id has extra info: $hash{$id}\n";
    }
    else {
        print "ID: $id has no extra info\n";
    }
}
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