# substitute in your dept codes, and a better hash name :)
my %deptCodesICareAbout=(
   RSRCH => 1,
   SALES => 1
);

# substitute in the right FILE, field list, and delimiter...
while(<FILE>) {
   my ($code, #whateverelse
      )=split/,/;
   if($deptCodesICareAbout{$code}) {
        # business logic
   }
}
[download]

I wish it were that simple! What I have are dept code *prefixes* which are not necessarily all the same length. For example, if our department codes were like:

ABCD123456 DEFG123456 DEFG998800 DEEE11223344

The code prefixes I have are like:

ABCD12 DEF DEEE11223

In other words, they can be any length. I tried using something like this:

foreach my $pattern (@patterns) {
   if (substr($fields[7],0,length($pattern)) eq $pattern) {
       ### Code here
       last;
   }
}
[download]

but that was slightly slower than the regex methods.

Ouch.

How many prefixes of each length, though? If you have many of a given length, maybe you could do something like this (writing support code to generate this HOH, of course):

my %prefixList=(
   3 => {DEF=>1, SRC=>1},
   6 => {ABCD12=>1},
  10 => {DEEEE11223},
);

#....
# inside the loop
foreach my $length(%prefixList) {
    if($prefixList{$length}->{substr($fields[7],0,$length)}){
        ### code here
        last;
    }
}
[download]

If the set of sizes isn't dynamic, you could make that an AOH, with some possibly empty hashes, I guess... You could also get rid of the loop and inline the check for each length, but I don't think that would save you much.

If you're only ever going to have 1 or 2 prefixes of a given length, then this isn't worth it. But given your initial description, I think with a LOT of prefixes and very few different lengths, this could start to pull ahead of the regex.
--
Mike