The commands control the periods Gcal respects. They can be partitioned into four major classes, namely single commands, special 3-Month mode commands, lists of commands and ranges of commands. Single commands and special 3-Month mode commands only create one calendar sheet, ranges of commands or list of commands create more than one calendar sheet per program run. If a list of commands is given, Gcal works sequentially on each single command given in the list, one by one. A range of commands is expanded first by Gcal and after expansion is done, Gcal works sequentially on each single command produced during the internal expansion step.
For understanding the notation used in the text below, mm is either a number, a month name or one of the special 3-Month mode commands ., .., .+ and .-. No lists or ranges of months or years can be created in case a special 3-Month mode command is given.
The range of mm is valid from 1 to 12 or valid from January to December. Both notations may be mixed. Month names may be abbreviated up to their first three characters. yyyy is a number. The range of yyyy is valid from 1 to 9999. A range (mm-mm or yyyy+yyyy or ...) must consist of two elements. A list (mm,...,mm or yyyy;...;yyyy or ...) must contain two elements minimum and may have any number of elements.
Here is a list of all ranges of commands, lists of commands and other command separator characters: