Is this what you want? 
my %common;
my ($first, @files) = @ARGV;

@common{ do { local @ARGV = ($first); <> } } = ();

for my $file (@files) {
    my %this;
    local @ARGV = ($file);
    @this{ grep exists $common{$_}, <> } = ();
    delete @common{ grep ! exists $this{$_}, keys %common};
}

print keys %common if keys %common;

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In reply to Re: find common lines in many files by happy.barney
in thread find common lines in many files by Anonymous Monk

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