It would help me to know what you are trying to do. The solutions offered thus far -- "sort -u" and using a hash -- both assume that you want to eliminate a line if it has a duplicate anywhere in the file. If all you want to do is eliminate successive repeated lines, something like this might be better: 
my $last = $_ = <>;
print;
while (<>)
        {
        print if ($_ ne $last);
        $last = $_;
        }

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In reply to Re: Checking LInes in Text File by Anonymous Monk
in thread Checking LInes in Text File by Anonymous Monk

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