Regex pattern for HH:MM:SS time string

Question

I want to parse a hh:mm:ss string. A simple one is ([0-1]?\\d|2[0-3]):([0-5]?\\d):([0-5]?\\d) which expects 2:3:24 or 02:03:24<

Answer 1

@Tim Pietzcker covers the OP's requirement for a HH:MM:SS parser where SS was mandatory, i.e.

• HH:MM:SS
• MM:SS
• SS

If you permit me to deviate from the OP's requirement for a bit, and consider a case where HH is mandatory, i.e.

• HH
• HH:MM
• HH:MM:SS

The regex I came up with was:

^([0-1]?\d|2[0-3])(?::([0-5]?\d))?(?::([0-5]?\d))?$

Let's break it down:

• ([0-1]?\d|2[0-3]) - matches for hours
• (?::([0-5]?\d))? - optionally matches for minutes
• (?::([0-5]?\d))? - optionally matches for seconds

Answer 2

^(?:(?:([01]?\d|2[0-3]):)?([0-5]?\d):)?([0-5]?\d)$

Explanation:

^                   # Start of string
(?:                 # Try to match...
 (?:                #  Try to match...
  ([01]?\d|2[0-3]): #   HH:
 )?                 #  (optionally).
 ([0-5]?\d):        #  MM: (required)
)?                  # (entire group optional, so either HH:MM:, MM: or nothing)
([0-5]?\d)          # SS (required)
$                   # End of string