Made the following changes:

1. Closed your files when you were done with them.;
2. Declared your variables (required under strict and intensely recommended for a huge list of reasons)

#!/usr/bin/perl

use strict;

my %csga = ();

my $moyr="12/2014";
$,="\t";
open(IN,"<COS_SGA_xref.txt");
while(<IN>) {
     chop;
     @_ = split(/\t/);
     $csga{$_[0]}=$_[1];
}
close IN;

open(IN,"<cc.txt");
open(OUT,">new_cc.txt");
for(my $i=0;$i<9;$i++) {$_=<IN>;}
my ($mo,$yr)=@_ = split(/\//,$moyr);
while(<IN>) {
     chop;
     @_ = split(/\t/);
     my $created=pop(@_);
     my ($mocr,$day,$yrcr)=@_ = split(/\//,$created);
     if($yrcr.$mocr >= $yr.$mo) {
          my $cc=$_[1];
          $cc =~ y/C_//d;
          splice(@_,3,1);
          shift(@_);
          print OUT $created,@_,$csga{$cc};
          print OUT "\n";
     }
}
close IN;
close OUT;

__END__
[download]

And the results:

D:\PerlMonks>test2.pl

D:\PerlMonks>
[download]

It created an empty output file called new_cc.txt. I presume that's because I did not have the input file COS_SGA_xref.txt.

I'm afraid additional debugging will be all guesswork unless you can provide sample input data.

At a guess, however, your problem is one of two things:

1. Since you didn't close IN, your attempt to open it again failed.
   • If you would check for errors on open, you could catch such things.
2. You only write output if this statement is true: if($yrcr.$mocr >= $yr.$mo). Maybe it never is?
   • A print statement right before the if could reveal the issue.

Made the following changes:

1. Checked status of open statements and displayed errors where appropriate;
2. Displayed suggested debugging statements.
   • NOTE: These might mess with your use of $_ and @_. I haven't used those in so long I've forgotten the rules.

#!/usr/bin/perl

use strict;

my %csga = ();

my $moyr="12/2014";
$,="\t";
if (!open(IN,"<COS_SGA_xref.txt"))
{
     print "ERROR:  Cannot open input file COS_SGA_xref.txt\n";
}
else
{
     while(<IN>) {
          # Using chop instead of chomp here makes me nervous - marine
+rsk
          chop;
          @_ = split(/\t/);
          $csga{$_[0]}=$_[1];
     }
     close IN;

     if (!open(IN,"<cc.txt"))
     {
          print "ERROR:  Cannot open input file cc.txt\n";
     }
     else
     {
          if (!open(OUT,">new_cc.txt"))
          {
               print "ERROR:  Cannot open output file new_cc.txt\n";
          }
          else
          {
               for(my $i=0;$i<9;$i++) {$_=<IN>;}
               my ($mo,$yr)=@_ = split(/\//,$moyr);
               while(<IN>) {
                    # Use of chop instead of chomp here makes me nervo
+us - marinersk
                    chop;
                    @_ = split(/\t/);
                    my $created=pop(@_);
                    my ($mocr,$day,$yrcr)=@_ = split(/\//,$created);
                    print "DEBUG:  -----------------------------\n";
                    print "DEBUG:  \$yrcr.\$mocr = [$yrcr.$mocr]\n";
                    print "DEBUG:      \$yr.\$mo = [$yr.$mo]\n";
                    if($yrcr.$mocr >= $yr.$mo) {
                         my $cc=$_[1];
                         $cc =~ y/C_//d;
                         splice(@_,3,1);
                         shift(@_);
                         print OUT $created,@_,$csga{$cc};
                         print OUT "\n";
                    }
               }
               # Cleanup
               close OUT;
          }
          # Cleanup
          close IN;
     }
}

__END__
[download]

And the results:

D:\PerlMonks>test3.pl
ERROR:  Cannot open input file COS_SGA_xref.txt

D:\PerlMonks>
[download]

Any further debugging requires information from you.

Good luck!

 
COS_SGA_xref.txt
195003    COS
195010    COS
500512    COS
500511    COS
520536    COS
550551    COS
550625    COS



cc.txt
01/31/2015                               Dynamic List Display         
+                              1

Controlling Area            C2
Date            01/01/1900  To    12/31/9999
Cost Center            All Cost Centers

    Cost Ctr    Description        CoCd    Profit Ctr    Person Respon
+sible    Created on

    6    PCS<>PCS MAIL CLOSED per B. Middleton        301    6000    G
+arrity, T.    05/24/2004
    30    COST CENTER 000001        170    112    Mac Crawford    08/3
+0/2004
    50    150BS - Balance Sheet C/C-(No RT)        150    112    Mac C
+rawford    08/16/2004
    60    COST CENTER 000001        160    112    Mac Crawford    08/1
+6/2004
    60    COST CENTER 000001        170    112    Mac Crawford    08/1
+6/2004
    70    COST CENTER 000001        170    112    Mac Crawford    08/1
+6/2004
    71    COST CENTER 000001        170    112    Mac Crawford    08/1
+6/2004
    74    COST CENTER 000001        170    112    Mac Crawford    08/1
+6/2004
    76    COST CENTER 000001        170    112    Mac Crawford    08/3
+0/2004
    77    COST CENTER 000001        170    112    Mac Crawford    08/3
+0/2004
    78    COST CENTER 000001        170    112    Mac Crawford    08/3
+0/2004
    80    State of NY        351    112    Bob Achettu    02/09/2006
[download]

Marinersk, thanks for your reply. I hope this works out. Sample data COS_SGA_xref.txt 195003 COS 195010 COS 500512 COS 500511 COS 520536 COS 550551 COS 550625 COS 560119 COS cc.txt 01/31/2015 Dynamic List Display 1 Controlling Area C2 Date 01/01/1900 To 12/31/9999 Cost Center All Cost Centers Cost Ctr Description CoCd Profit Ctr Person Responsible Created on 6 PCS<>PCS MAIL CLOSED per B. Middleton 301 6000 Garrity, T. 05/24/2004 30 COST CENTER 000001 170 112 Mac Crawford 08/30/2004 50 150BS - Balance Sheet C/C-(No RT) 150 112 Mac Crawford 08/16/2004 60 COST CENTER 000001 160 112 Mac Crawford 08/16/2004 60 COST CENTER 000001 170 112 Mac Crawford 08/16/2004 70 COST CENTER 000001 170 112 Mac Crawford 08/16/2004 71 COST CENTER 000001 170 112 Mac Crawford 08/16/2004 74 COST CENTER 000001 170 112 Mac Crawford 08/16/2004 76 COST CENTER 000001 170 112 Mac Crawford 08/30/2004 77 COST CENTER 000001 170 112 Mac Crawford 08/30/2004 78 COST CENTER 000001 170 112 Mac Crawford 08/30/2004 80 State of NY 351 112 Bob Achettu 02/09/2006 80 State of NY 301 112 Bob Achettu 02/09/2006