A rough outline for your code would be:

1. open F1
2. open F2
3. Slurp F2 into an array
4. For every line in F1 (perhaps using I/O Operators in a while loop)
   1. Check if the variable containing F2 contains the line in question, perhaps using a regular expression and grep.
   2. If yes, print the line.

If you do not know how to do any of these steps and have read the documentation, post specific questions with code (or at least pseudocode), sample input and expected output. Perlmonks is here to help you help yourself.

I followed the steps,it solved the problem..Thanks a lot everyone

how do we do this

Another solution is to use the Unix utilities sort and comm.

What have you tried? What part do you have trouble understanding?

...roboticus

awk 'NR==FNR{a[$0]=$0;next}$0 in a{print}' file2 file1
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$ comm -12 <(sort file1) <(sort file2)
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And a Perl solution that does the same:

use File::Slurp;

my @a1 = sort {$a cmp $b} read_file shift;
my @a2 = sort {$a cmp $b} read_file shift; 

while (@a1 && @a2) {
    my $cmp = $a1[0] cmp $a2[0];
    print $a1[0] if !$cmp;
    shift @a1 if $cmp <= 0;
    shift @a2 if $cmp >= 0;
}
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grep -f F2 F1
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