You need to edit your post and add code tags. Right now it's all smooshed together, so it's unreadable.

I'm looking to find common lines between two files (mail.fil) and (THIDSerrs). I then want to eliminate the common lines from the one file, mail.fil.

#!/usr/local/perl-5.12.3/bin/perl
use strict;
use warnings;
open FILE,"< mail.fil";
my @oralines=<FILE>;
close FILE;
#print @oralines;
open FILE,"<THIDSerrs";
my @errs = <FILE>;
close FILE;
#print @errs;
my @subarray = ();
foreach my $oralines(@oralines)
{
  foreach my $errs(@errs)
  {
  push @subarray, $oralines if grep /$errs/, @oralines;
  }
}
print "@subarray \n";
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Hope this is more readable - I'm new at this.

I'm looking to find common lines between two files

$ man comm
NAME
       comm - compare two sorted files line by line

SYNOPSIS
       comm [OPTION]... FILE1 FILE2

DESCRIPTION
       Compare sorted files FILE1 and FILE2 line by line.

       With  no  options,  produce  three-column  output.  Column one 
+contains
       lines unique to FILE1, column two contains lines unique to  FIL
+E2,  and
       column three contains lines common to both files.

       -1     suppress lines unique to FILE1

       -2     suppress lines unique to FILE2

       -3     suppress lines that appear in both files

       --help display this help and exit

       --version
              output version information and exit

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Trying to do all of this in Perl - management doesn't want UNIX commands so I can port this to Windows machines. Thanks.

By doing a 'Super Search', (located at the top of any PerlMonks page here), with the words 'find common lines', you will find similiar problems and solutions.

Only, they find lines in common rather than unique. But its not difficult to figure this the difference, I believe.

If the THIDS file isn't too large for your memory, you could read it into a hash to check against the 'mail.fil' for differences.

#!/usr/local/perl-5.12.3/bin/perl
use strict;
use warnings;

open my $THIDS,"<", "THIDSerrs" or die "Could not open 'THIDSerrs' for
+ reading. $!";
my %data = map {$_ => 1} <$THIDS>;
close $THIDS or die "Unable to close 'THIDSerrs' - reading. $!";

open my $mail, "<" , "mail.fil" or die "Could not open 'mail.fil' for 
+reading. $!";
open my $out, ">", "whatever.dat" or die "Unable to open 'whatever.dat
+' for write. $!";

while (<$mail>) {
    print $out unless $data{$_};
}

close $mail or die "Unable to close 'mail.fil' - reading. $!";
close $out or die "Unable to close 'whatever.dat' from writing. $!";
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Thanks. I'll work on this tonight