Formatting a Julian Date [Julian Day / Day of Year] in Unix

This is one of those commands that’s so simple once you recall it that you’ll smack yourself for not knowing it.

If you’re ever in doubt, man date.

# displays the 2-digit year + day of the year, Jan 14, 2011 = "11014"
date +%y%j

# sets filename to MyFilename + 2-digit year + day of the year
# Jan 14, 2011 = MyFilename11014
filename=MyFilename`date +%y%j`

Remember to use lowercase ‘y’. Uppercase ‘Y’ will give you a 4-digit year.