The options processed by Gcal can be grouped into four major option classes. The options of the common option class are the standard options all GNU software should implement at least partially. The global option class contains options which affect the program output. The options of the calendar option class control the calendar layout, and the options of the fixed date option class control the fixed date layout and intensity.
Gcal supports both short-style options and GNU long-style options. Traditional short-style options are indicated by a single switch character, and trailed by the option character itself and perhaps a modifier or an argument. The most single character options1 can be composed into a single command line word: -Ax is equivalent to -A -x. GNU long-style options are indicated with ‘--’, and trailed by the mnemonic option name itself and perhaps an argument. Long-style options and their arguments may be abbreviated if done unambiguously. When a long-style option takes an argument, connect the option name and the argument with ‘=’.
Brackets ([ and ]) indicate in the following tables, that an option takes an optional argument. The ‘|’ character is used to separate several arguments from each other.
Gcal processes the GNU long-style options in a special, non-standard way. There are five different types of long-style options:
Traditional short-style options differ as follows:
 Unless they take an argument.