Ignore (most) of this!

That's the trouble with running code in your head. You don't always notice scoping issues. And answer to the question at the end would still help though.

Did you tidy your code up for posting? I ask because there is a logic error in what you've posted that (I think) means that it cannot do what you are wanting it to do.

    if(/3_prtnm_/){
        @tmp = split(/3_prtnm_/);
        $unit_count = &trim($tmp[1]);
    }
    elsif(/2_tname_/){
        @tmp = split(/2_tname_/);
        $testname = &trim($tmp[1]);
        if(exists $param_flag{$testname}){
            $testFound = 1;
        }
    }
    elsif($testFound){
        if(/2_mrslt_/){
            @tmp = split(/2_mrslt_/);
            $paramVal = &trim($tmp[1]);
            print OUT "$testname,$unit_count,$paramVal\n";
            $testFound = 0;
        }
    }
[download]

1. You will only ever print anything to the output file if $testFound is true.
2. But $testFound is only ever set true inside another branch of the same if/else cascade?
3. The same is also true for the values of both $testname and $unit_count

Also, how many keys are there in %param_flag and what do they look like?

If you can clarify those, I'll try and adapt the logic of your subroutine to use the big string technique I mentioned above.