EDIT: holli was faster.

It's the same as:

my $tempport;
if ($args{DOUBLE_BYTE} =~ /y/i) {
  $tempport = DB_CATPORT;
} else {
  $tempport = SB_CATPORT;
}
[download]

See http://perldoc.perl.org/perlop.html#Conditional-Operator for details.