Try the following code. The output is on STDOUT, but you should have no problem modifying ti to output to a file if you need it. The script uses a %seen hash as lookup table to avoid print out duplicates.

#!/usr/bin/perl -Tw

use strict;

open (my $myfile, "./prova.txt");

my %seen;

while (<$myfile>) {
    chomp;
    my ($c1, $c2) = split(/\|/);
    unless (defined $seen{$c1}) {
        print "$c1$c2\n";
        $seen{$c1} = 1;
    }
}

close ($myfile);
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Hope this helps!

Michele.