Shell Programming and Scripting

I originally had a shell script that did a grep 10 times to pull out the number of times a certain pattern occured in a file: ie...

aOccurances=`grep aPattern file|wc -l`
bOccurances=`grep bPattern file|wc -l`
...
...
...
fOccurances=`grep fPattern file|wc -l`

As the file got bigger with more occurances of {a,b...,f} the script became extremely slow. I tried to rewrite the script in perl to open the file once and do pattern matching instead: ie...

open (FILE, FILENAME) ||die "Can't open: $!";
aCount=0;
bCount=0;
...
...
fCount=0;

while(<FILE>){
aCount++ if /aPattern/;
bCount++ if /bPattern/;
...
...
fCount++ if /fPattern/;
}

This appeared to run even slower even though I am opening the file only once. Any ideas on why and how to make this faster? Thanks.