I needed a regular expression to correctly parse ISO 8601 format dates and times. The standard includes many alternative representations, but I was particularly concerned about the subset of ISO 8601 formats allowed in XML.
Edit 26 May 2009: If you want full ISO compliance, check out the expression Cameron Brooks lists in his comment below.
Paul Ward had posted a date parsing expression on the RegExLib site. I extended it a bit to handle times and time zones. I’m pretty sure they work, though it can be hard to tell sometimes. (See Jeff Atwood’s Now You Have Two Problems.)
ISO date
^(\d{4})\D?(0[1-9]|1[0-2])\D?([12]\d|0[1-9]|3[01])$
ISO time
^([01]\d|2[0-3])\D?([0-5]\d)\D?([0-5]\d)?\D?(\d{3})?$
ISO offset
^([zZ]|([\+-])([01]\d|2[0-3])\D?([0-5]\d)?)?$
ISO date and time
^(\d{4})\D?(0[1-9]|1[0-2])\D?([12]\d|0[1-9]|3[01])(\D?([01]\d|2[0-3])\D?([0-5]\d)\D?([0-5]\d)?\D?(\d{3})?)?$
ISO date, time, and offset (the works)
^(\d{4})\D?(0[1-9]|1[0-2])\D?([12]\d|0[1-9]|3[01])(\D?([01]\d|2[0-3])\D?([0-5]\d)\D?([0-5]\d)?\D?(\d{3})?([zZ]|([\+-])([01]\d|2[0-3])\D?([0-5]\d)?)?)?$
If you find it useful — or find a bug — let me know.
Edit 21 Jan 2008: Stan James sent us some enhancements to the validation routines. Here’s what he had to say:
I needed a RegExp that could detect ISO dates with varying precision. (e.g. “1945″, “1945-12″, “1945-12-01″, “1945-12-01T12:15″ etc..)
For future readers, here’s what I came up with:
Date only
^[0-9][0-9][0-9][0-9](-[0-1][0-9](-[0-3][0-9])?)?$Date and Time
^[0-9][0-9][0-9][0-9](-[0-1][0-9](-[0-3][0-9](T[0-9][0-9](:[0-9][0-9](:[0-9][0-9])?)?)?)?)?$
Thanks, Stan!