This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
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 environment variables shall affect the execution of cal:
Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1‐2008, Section 8.2, 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.
Earlier versions of this standard incorrectly required that the command:
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.
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .
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