CL-STRFTIME is a Common Lisp compiler for the strftime “language.” FORMAT-TIME takes four arguments: a stream, a strftime-style control string, a time (defaults to now), and a time zone (defaults to here). (cl-strftime:format-time t "%D" (get-universal-time)) => 02/12/12 The stream argument may be NIL or T, as for FORMAT. The time argument may be a universal time or a LOCAL-TIME timestamp. The time zone should be NIL, for here; T, for UTC; or a time zone object in LOCAL-TIME'S format. The other exported function, MAKE-TIME-FORMATTER, is to FORMAT-TIME as FORMATTER is to FORMAT. FORMAT-TIME also understands a number of named formats. To use a named format, pass a keyword in place of the control string. (cl-strftime:format-time t :rfc-3339 (get-universal-time)) => 2012-03-19T06:16:29Z FORMAT-TIME understands the following flags and directives: FLAGS - Do not pad _ Pad with spaces 0 Pad with zeros # Toggle case ^ Upcase DIRECTIVES %% Literal percent sign %A Weekday (Sunday) %a Abbreviated weekday (Sun) %B Month (January) %b Abbreviated month (Jan) %C Century (20) %d Day of month (01-31) %D Same as %m/%d/%y %e Same as %_2d %F Same as %Y-%m-%d %G ISO 8601 year %g ISO 8601 year in century %h Same as %b %H Hour (01–24) %I Hour (01–12) %j Day of year (001-366) %k Hour ( 1-24) %l Hour ( 1-12) %m Month (01-12) %M Minute (00-59) %n Literal newline %p AM or PM %P am or pm %r Same as %I:%M:%S %p %R Same as %H:%M %s Epoch time %S Second (00-59) %t Literal tab %T Same as %H:%M:%S %u Day of week (weeks start on Monday) %U Week number %V ISO 8601 week number %w Day of week %W Week number (weeks start on Monday) %y Year of century (12) %Y Year (2012) %z RFC 2822 timezone %Z Name of timezone NAMED FORMATS (Formats on the same line are synonyms.) :ARPA :EMAIL :RFC-822 :ASCTIME :CTIME :COOKIE :HTTP :RFC-2616 :NEWS :RFC-850 :USENET :RSS :RFC-2822 :RFC-1036 :RFC-2086 :RFC-1132 :UNIX :W3C :HTML :RFC-3339 :XML :ATOM CL-STRFTIME goes to great lengths to be compatible with strftime. In fact it uses generative testing to ensure its results match those generated by `date`.