It shouldn't be that much trouble. If the OP script works most of the time (except when there's a file with a blank line), then just adding the "next" statement as shown (first line of code inside the while loop) should work all the time:

#!/usr/bin/perl -w
use strict;
use warnings;
use diagnostics;
my %saldi;
while (<>) {
    next unless ( /,/ );  ## add this line
    my @cellen = ( split /,/, )[ 3, 4 ];
    $saldi{ $cellen[0] } += $cellen[1];
    if ( eof(ARGV) ) {
        $ARGV =~ m/^(\S+)\.txt/;
        print "$1\n";
        foreach my $name ( keys %saldi ) {
            print "\t$name\t$saldi{$name}\n";
        }

    }
}
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