正则表达式强制和可选组

Question

I'd like to create a regex with groups which must be included in the string and groups which are only optional. I'm using c# for that.

My Target String looks like this

    ##my_first_string-2#E+1##
    ##my_second_string-2#E-2##
    ##my_third_string__##

I have the following requirements :

• ## is mandatory at the beginning and the end (but this is not necessarily the beginning or end of line)
• the string between ## and # (or ## ) is mandatory as well
• E+{Numbers} or E-{Numbers} is optional

So far i have come up with

(##.*?##)

=> to match all Characters in between the 2 ## ##

(##)([A-Za-z\-])\w+(##)

=> to match the first string. But for some reason this captures ##my_first_string-2 and not only my_first_string-2

Could you help me create a regex for my requirements?

Answer 1

Try this:

##([^#]+?)(#E[+-][0-9]+)?##

The important part is:

(#E[+-][0-9]+)?

The "?" quantifier specifies zero or one occurrence

Replace the following with the character requirements for the string, currently its just "all except #"

([^#]+?)

Hope this helps.