Mac/Linux: Need to quickly check dates and don't have a calendar app ready? You can generate calendar data for any month in an instant with a quick terminal command.
Just type this:
cal 10 2013
In fact, you only need to type cal to generate a calendar for the current month. If you want a different month, however, just type cal and then the number of the month. If you want to specify a year other than the current year, type cal then the number of the month and then the year, all separated by a space. The result? A nicely formatted text-based calendar like the one you see pictured above.
5 Most Useful Terminal Command Utilities [Using Mac]