After i declare the variable as you suggested, it comes out another error, said 'use of uninitialized value $A in concatenation <.>.....'
#Main body
while (my $line = <TEMP>)
{
my $A;
my $B;
my @column = split (/,/,$line);
if ($column[4] < $column[7])
{ $A = $direction[0];
}else {$A = $direction[1]; }
if ($column[5] < $column[8])
{ $B = $direction[2];
}else {$B = $direction[3]; }
my $dir = $A.$B;
print OUTPUT $column[4],$comma,$column[5],$comma,$column[7],$comm
+a,$column[8],$comma,$dir,$comma,$nline;
}