> some_binary.out A

   or 

  > some_binary.out B

##</code><code>##

#!/usr/bin/perl -w       

# aboved changed thanks to Mandrake

use Data::Dumper;

my $param  = 'A';  
# When I replace 'A' with 'B', it gives no output


my @output = `some_binary.out $param`;
chomp @output;

print Dumper \@output;

# gives $VAR1 = []; with 'B'