Are you sure you did
my $OID = "1.2.3.6.9.5.6.8"
and not
my $OID = "1.2.3.6.9.5.6.8\n"?

If you did my $OID = <SOME_HANDLE>;, you did the latter. To remove the trailing newline, use chomp: chomp( my $OID = <SOME_HANDLE> );