I have a question about regexes in Java, though I think this might apply to other languages as well.
I have a regex to parse time from a field where user may enter something like 4d 8h 42m. Of course, I want to make it as flexible as possible, so that user should not be obliged to type all numbers (and enter a mere 15h for instance).
My regex is quite satisfactory concerning that point: (?:([\d]+)d)?[\s]*(?:([\d]+)h)?[\s]*(?:([\d]+)m)?
Now my problem is that it will also match an empty string, though I would like it to ensure that at least one time-unit is filled.
The current solution would be to arbitrary choose one of them to be mandatory, but I am not satisfied with it since mandatory field is what I am trying to avoid.
Also, making an or does not suit me, since I would have to test groups when parsing the regex afterwards, instead of just accessing group(1) for days, group(2) for hours, …
(This is what I think of when speaking of an or : (?:([\d]+)d[\s]*(?:([\d]+)h)?[\s]*(?:([\d]+)m)?|(?:([\d]+)d)?[\s]*([\d]+)h[\s]*(?:([\d]+)m)?|(?:([\d]+)d)?[\s]*(?:([\d]+)h)?[\s]*([\d]+)m), to be understood as days mandatory or hours mandatory or minutes mandatory).
So how could I modify my regex to make sure that at least one of my now-non-capturing group is not empty, be it days, hours or minutes?
You can use a look-forward assert to ensure that at least one of
dhormappears.