RegEx to match 123.45 and E123.4 and V12.34

Question

I'm trying to create a RegEx that matches the 3 patterns listed above. I can somewhat create a working RegEx for any of those 3 but my problem is creating one that works with all 4 of those. The allowed values are below, where D is any digit and the '.' is never present as a trailing character (i.e. DDD. wouldn't be valid). Also the V and E refer to those specific characters.

• ddd
• ddd.d
• ddd.dd
• Vdd
• Vdd.d
• Vdd.dd
• Eddd
• Eddd.d

Everything else should be invalid, such as:

• d
• dd
• V
• Vd
• Vdd. (trailing '.')
• E
• Ed
• Edd

I'm not great with RegEx, but I could describe part of this pattern for the entries that start with V as the following:

V[0-9]{2,2}(\.[0-9]{1,2})?

I could write very similar statements for the all digit portion of entires and E prefix portion of entries. The problem is how to combine all 3 into a RegEx that doesn't make my head spin to read. What's a good RegEx to match all 3 patterns?

EDIT: I forgot to include the format Vdd.dd

Answer 1

(E\d|(V|\d))\d{2,2}(\.\d)?(?(2)\d?|)

E with one digit, or V, or a single digit, followed by two digits, then the usual decimal stuff.

E has to have three non decimal digits, V has to have 2, and digits by them selves have to have three.

If the V or single digit match at the start (I.E. Not 'E') then an extra digit is allowed on the rear.

Answer 2

(\d{3}(\.\d{1,2})?)|(V\d{2}(\.\d{1,2})?)|(E\d{3}(\.\d)?)

EDIT: Some explanation: I just matched all 3 different formats:

\d{3}(\.\d{1,2})?

says three digits optionally followed by a period matched with 1 or 2 digits.

V\d{2}(\.\d{1,2})?

says V followed by two digits with optional period and one or two digits

E\d{3}(\.\d)?

says three digits followed by an optional period with a single digit

Then I just surrounded each with () and combined them all with | (or).

Answer 3

Nothing wrong with having three different regular expressions, is there?

\d{3}(.\d{1,2)?
V\d{2}(.\d)?
E\d{3}(.\d)?

And this will probably be more maintainable in the future.

Answer 4

If Eddd would be invalid it would be much easier:

[EV\d]\d{2}(\.\d{0,2})?

Similarly if Vddd was valid:

[EV\d]\d{2,3}(\.\d{0,2})?

Matching exactly what you have is a bit harder:

(\d{3}(\.\d{1,2})?)|(V\d{2}(\.\d)?)|(E\d{3}(\.\d)?)

Make sure you test for exact match otherwise things like

V123.1

Will match as

V12