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use warnings;
use strict;

 $src_filename = $ARGV[0];
 $var_filename = $ARGV[1];
 $tgt_filename = $ARGV[2];
 $mac_filename = $ARGV[2];

die "Usage: four arguments\n" unless $#ARGV == 3;
my ($src_filename,$var_filename,$tgt_filename,$mac_filename) = @ARGV;

while (defined my $line = <IFILE>) { 
 chomp; # remove \n from the end of the line
 ...
}

   #Read only 1 - 72 columns data
   $Line =~ /.{72}/;
   $Line = $&;
   $Line = $Line."\n";

   $Temp = $Line;

   #Remove evrything after column 40 fromt he code
...
   $Line = $&; 
   chomp($description);
   $description =~s/\s+$//g;

   $Line =~s/\(/\'/g;
   $Line =~s/\)/\'/g;

...
          }
      }
     }

if($line =~/([^\s]+)\s+(DC|DS|EQU)\s+(A|X|C|H|F|D|0X|0D|0C)+(L)*([^\'\
+(\s]+)*(\'(.+)\')*\s*/i) {
 ($line,my $description) = ($line=~/^(.{40})(.*)\s+$/); # do the actua
+l $line modification only there
...
  length $line > 0 && push @Tgt_File_Array,(join " ",(split ' ',$line)
+[0,1]);
 }
}