declare a hash (e.g. "my %lines."
open the first input file
while reading the first input one line at a time
   use the line as a hash key and assign "1" as the hash value
close the file

open output.file1 to hold "matching lines"
open output.file2 to hold "distinct lines"

open the second input file
while reading the second input one line at a time
   if the current line exists as a hash key and the hash value is "1"
     print this line to the "matching lines" file
     increment the hash value
   otherwise
     print this line to the "distinct lines" file (maybe include the f
+ile name)

having read all input, now loop over all the keys of the hash
   if the hash value assigned to this key is still "1"
     print this hash key to the "distinct lines" file (maybe include t
+he file name)
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Thankyou...Hi i have written the code as per your algorithm

#!/usr/bin/perl
use strict;
use warnings;
my %lines;

open F1, "File.txt";
    while(my $result= <F1>)
    {
      $lines{$result}=1;
    }
    close(F1);

open (OF1, ">match.txt");
open (OF2, ">diff.txt");

open F2,"File2.txt";

while(<F2>)
{
if ($lines{$_}==1)
{
 print OF1 $lines;
 $lines++;
}
els
{
print OF2 $lines;
}
}

close OF1;
close OF2;
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and i am getting this error: Global symbol "$lines" requires explicit package name at line.pl line 21,22,26. i am gng throu the tutorials..

You have declared a hash, my %lines;, but then you are trying to use that variable as if it were a scalar in this line:

 print OF1 $lines;
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You probably want:

 print OF1 $lines{$_};
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Same for OF2.

Also, "els" is a typo: should be "else".

$lines++; is also a problem.

We strongly recommend that you use strictures (use strict; use warnings;) at the start of all the Perl you write. They give you early warning of a wide range of issues.

We also like it if you tell us up front if you are doing homework or are doing this as a learning exercise (this smells like a homework question) so that we can tailor our replies to help you learn.

Your first attempt is almost ok for small files, although the syntax is not correct and there is a problem. A syntax corrected version would look somewhat like:

use strict;
use warnings;

my $F1 = <<F1;
name   value
n1       001
n2       002
n3       003
n4       004
F1
my $F2 = <<F2;
name     value
n5       005
n2       002
n3       003
n8       008
F2

open FH1, '<', \$F1 or die "Failed to open F1: $!";
open FH2, '<', \$F2 or die "Failed to open F2: $!";

my @f1= <FH1>;
my @f2= <FH2>;

for my $f1Line (@f1) {
    for my $f2Line (@f2) {
        if ($f1Line eq $f2Line) {
            print "Same: $f1Line";
        } else {
            print "Diff: $f1Line";
        }
    }
}

close(FH1);
close(FH2);
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which prints:

Diff: name   value
Diff: name   value
Diff: name   value
Diff: name   value
Diff: name   value
Diff: n1       001
Diff: n1       001
Diff: n1       001
Diff: n1       001
Diff: n1       001
Diff: n2       002
Diff: n2       002
Same: n2       002
Diff: n2       002
Diff: n2       002
Diff: n3       003
Diff: n3       003
Diff: n3       003
Same: n3       003
Diff: n3       003
Diff: n4       004
Diff: n4       004
Diff: n4       004
Diff: n4       004
Diff: n4       004
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which is not quite what you want and becomes horribly slow when the files get big.

Generally however this is a tricky problem to solve because good solutions require knowledge of the size and nature of the contents of the files. A common key to the solution involves using hashes (see perldata) to keep information about data that has been seen before.

At this point you can either play with your current code, or learn about hashes and possibly come back for more instruction.