use strict;
use warnings;
use Text::CSV;

die "usage: $0 SourceFile TargetFile MappingFile\n" if @ARGV < 3;

my $csv = Text::CSV->new({ auto_diag=>1, binary=>1, eol=>"\n" });

my %map;
open my $MAP, '<', $ARGV[2] or die "Can't read $ARGV[2]: $!";
while (my $row = $csv->getline($MAP)) {
   my ($old_cost, $old_act, $new_cost, $new_act) = @$row;
   $map{$old_cost}{$old_act} = [$new_cost, $new_act];
}
close $MAP;

open my $IN, '<', $ARGV[0] or die "Can't read $ARGV[0]: $!";
open my $OUT, '>', $ARGV[1] or die "Can't write $ARGV[1]: $!";
while (my $row = $csv->getline($IN)) {
   if (my $new = $map{$row->[6]}{$row->[7]}) {
      $row->[6] = $new->[0];
      $row->[7] = $new->[1];
   }
   $csv->print($OUT, $row);
}
close $IN;
close $OUT;
[download]

Re: Give a man a fish...
Sometimes, you have to show him what a fish looks like first.

First , thanks for being patient and youyr help. i ran the code its giving the below Error and nothing is coming up in the Target file.

=========================================================================================

C:\Users\sksingh>perl "C:\Users\sksingh\Documents\Barrick Work\Perl\GC
+OA\newway.pl" "C:\Users\sksingh\Documents\Barrick Work\Perl\GCOA\NAAC
+T.txt" "C:\Users\sksingh\Documents\Barrick Work\Perl\GCOA\NAACTDEPEND
+.txt" "C:\Users\sksingh\Documents\Barrick Work\Perl\GCOA\FINALMAPDEPE
+NDENT.txt"
# CSV_XS ERROR: 2023 - EIQ - QUO character not allowed @ rec 1840 pos 
+12 field 1
[download]

=========================================================================================

First, <code> tags are easy to use. When you're entering your post, type something like this:

---

<code>

for my $i (1 .. 10) {
   print "And a $_,\n";
}
[download]

</code>

---

And it will come out looking nice. If you leave off the <code> and </code>, it will be all jumbled together and people will yell at you. Also, instead of typing a row of equal signs like you've been doing, you can instead use <hr>, which stands for horizontal rule.

Second, as runrig says, there's probably something weird in your input file. Try looking at line 1840. Try making a smaller input file to make testing easier.

Maybe there's something wrong with record 1840 in your input file?