I have this string
*** Sampled system activity (Sun Oct 31 10:57:41 2021 0100) (1007.04ms elapsed) ***\n
I need to extract 10:57:41
I try with
^([0-1]?\d|2[0-3])(?::([0-5]?\d))?(?::([0-5]?\d))?$
or
^(?:(?:([01]?\d|2[0-3]):)?([0-5]?\d):)?([0-5]?\d)$
But it doesn't works
CodePudding user response：
Keeping it simple, I suggest just using:
\b\d{1,2}:\d{2}:\d{2}\b
It is unlikely that anything in your input text other than a time component would match this. Here is a demo showing the pattern working.
CodePudding user response：
Your pattern does not match due to the anchors ^ and $ which assert the start and the end of the string.
If you remove the anchors, you have ([0-1]?\d|2[0-3])(?::([0-5]?\d))?(?::([0-5]?\d))? which will give partial matches as the last 2 groups are optional.
If you remove the ? from the groups, you are left with superfluous non capture groups, which can be omitted as well. Now you have ([0-1]?\d|2[0-3]):([0-5]?\d):([0-5]?\d)
For a match only, you can omit the capture groups, and turn the first capture group in a non capture group. To prevent partial matches, you can add word boundaries \b
The simplified pattern:
\b(?:[01]?\d|2[0-3]):[0-5]?\d:[0-5]?\d\b