You might be interested in Building Regex Alternations Dynamically so that you don't have to loop over your IDs.
use warnings;
use strict;
use Data::Dump;
my @ids = ("a", "b", "c", "d", "e", "f", "g",);
my ($regex) = map {qr/$_/} join '|', map {quotemeta}
sort { length $b <=> length $a or $a cmp $b } @ids;
my %counts = map { $_ => 0 } @ids;
while (<DATA>) {
if ( my ($id) = /($regex)/ ) {
$counts{$id}++;
}
}
dd \%counts;
# outputs "{ a => 1, b => 2, c => 2, d => 3, e => 0, f => 3, g => 0 }"
__DATA__
a
b
b
NO ID HERE
c
c
d
d
d
f
f
f