Hi Ken This code worked for me after I put last line: printf "%s %s\n", $_, $uniq{$_} for sort keys %uniq; before closing parenthesis. Thanks a million:)

"This code worked for me after I put last line ... before closing parenthesis. Thanks a million"

Whilst I appreciate the thanks, it sounds like you've introduced a (possibly subtle) bug. The basic logic for my code is:

Declare hash

SINGLE BLOCK (reading one file):
    Populate hash 

LOOP BLOCK (reading all other files):
    Remove data that isn't common from hash

Print hash data
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If you move the Print operation to LOOP BLOCK, you'll get multiple (24) groups of output. That's not what you want, and it would have been plainly obvious if you'd done that, so you've probably done something different to what you've described.

You've said "I am very beginner of perl" in a couple of places. I suspect you haven't understood the anonymous block I used in SINGLE BLOCK and ended up with logic more like this:

Declare hash

start SINGLE BLOCK
    Populate hash 

    LOOP BLOCK

    Print hash data
end SINGLE BLOCK
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An anonymous block is just code wrapped in braces:

{
    # code here
}
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I've used it to provide a limited lexical scope. The variables ($fh, $k and $v) that I've declared in that block, only exist in that block; they are quite different to, and cannot interfere in any way with, the similarly named variables elsewhere in the code. There's also an additional benefit: when $fh goes out of scope, Perl performs an implicit close.

Anyway, while that's probably useful information you can add to your "beginner of perl" knowledgebase, it's very much guesswork on my part with respect to whatever modifications you made to my original code. If you post your changes, I can provide more concrete feedback.

— Ken

I am very grateful for all the useful explanations you have provided. As you know, I am very beginner of perl, i tried to modify your provided code, because it didn't worked for me. I can see the logic for your code. But please let me ask you something. Following of your code isn't giving any output when i use it for 25 files. Please tell me how to fix it.

#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

my @files = glob 'pm_1206312_in*';
my %uniq;

{
    open my $fh, '<', shift @files;

    while (<$fh>) {
        my ($k, $v) = split;
        $uniq{$k} = $v;
    }
}

for my $file (@files) {
    my %data;
    open my $fh, '<', $file;

    while (<$fh>) {
        my ($k, $v) = split;
        $data{$k} = $v;
    }

    for (keys %uniq) {
        delete $uniq{$_} unless exists $data{$_} and $uniq{$_} eq $dat
+a{$_};
    }
} 

printf "%s %s\n", $_, $uniq{$_} for sort keys %uniq;
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