The reason of the weird result is the setting of this inconspicuous variable: 
$/ = undef;

[download]

It enables the "slurp mode", i.e. <FILE> reads the whole file into $_. But you then check 

if (/$i/g)

[download]
which only runs once.

You can fix it in several ways:

  1. keep the $/ unchanged. It will read the file line by line and update the variable appropriately.
  2. replace the if by while, it will run the increment for each match
  3. create a regex from all the ids and match all of them at once: 
    my $regex = join '|', map quotemeta, @ids;
while (<FILE>) {
    $counts{$1}++ if /($regex)/;
}

    [download]

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: Perl beginner's issue with hash by choroba
in thread Perl beginner's issue with hash by Maire

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