cal - print a calendar
[XSI] cal [[month] year]
The cal utility shall write a calendar to standard output using the Julian calendar for dates from January 1, 1 through September 2, 1752 and the Gregorian calendar for dates from September 14, 1752 through December 31, 9999 as though the Gregorian calendar had been adopted on September 14, 1752.
If no operands are given, cal shall produce a one-month calendar for the current month in the current year. If only the year operand is given, cal shall produce a calendar for all twelve months in the given calendar year. If both month and year operands are given, cal shall produce a one-month calendar for the given month in the given year.
The following operands shall be supported:
- Specify the month to be displayed, represented as a decimal integer from 1 (January) to 12 (December).
- Specify the year for which the calendar is displayed, represented as a decimal integer from 1 to 9999.
The following environment variables shall affect the execution of cal:
- Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error, and informative messages written to standard output.
- Determine the format and contents of the calendar.
- Determine the location of message catalogs for the processing of LC_MESSAGES.
- Determine the timezone used to calculate the value of the current month.
The standard output shall be used to display the calendar, in an unspecified format.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- Successful completion.
- An error occurred.
Note that:cal 83
refers to A.D. 83, not 1983.
Earlier versions of this standard incorrectly required that the command:cal 2000
write a one-month calendar for the current calendar month (no matter what the current year is) in the year 2000 to standard output. This did not match historic practice in any known version of the cal utility. The description has been updated to match historic practice. When only the year operand is given, cal writes a twelve-month calendar for the specified year.
A future version of this standard may support locale-specific recognition of the date of adoption of the Gregorian calendar.
XBD Environment Variables
First released in Issue 2.
The DESCRIPTION is updated to allow for traditional behavior for years before the adoption of the Gregorian calendar.
SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.
POSIX.1-2008, Technical Corrigendum 1, XCU/TC1-2008/0074  and XCU/TC1-2008/0075  are applied.
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