my %userData;

open(inData, $data);

while (<inData>) {
    chomp;
    $line = $_;
    if ($line =~/^GC/){
       my $ACTNUM =  substr $line, 11, 9 ;
       my $ref =  substr $line, 0, 3 ;
       $userData{$ACTNUM}{$ref} = $line;
    }
}
for my $ACTNUM (sort keys %userData) {
  $line = $userData{$ACTNUM}{GCA};
  $ACCTNUM = substr $line, 11, 9;
  $FIRM_ID = substr $line, 660, 1;
  $CURR = substr $line, 661, 3;
  print "$CURR,$ACCTNUM,$FIRM_ID\n";
}


##</code><code>##

This prints out what I want via Dumper:

my $data = "GCUS.GCUS";my %userData;open(inData, $data);while (<inData>) {    chomp;
    $line = $_;
    if ($line =~/^GC/){
       my $ACTNUM =  substr $line, 11, 9 ;
       my $ref =  substr $line, 0, 3 ;
       push @{ $userData{$ACTNUM} }, $ref = $line;


    }
}

Here is where I get stuck and cant seem to understand the perl doc:

for  $ACTNUM (sort keys %userData) {
#########GCA##############
 my  $line = $userData{$ACTNUM}{GCA};
  $ACCTNUM = substr $line, 11, 9;
  $FIRM_ID = substr $line, 660, 1;
  $CURR = substr $line, 661, 3;