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Regular expression with conditional repetition

I have the following regex:

^((_[a-zA-Z0-9]|[a-zA-Z])+((?<bracket>\[)[0-9]+(?<-bracket>\])(?(bracket)(?!)))?)$

I want this to repeat if there is a dot ( .

)

I know I can repeat an expression like this by adding a dot ( .

)

^((_[a-zA-Z0-9]|[a-zA-Z])+((?<bracket>\[)[0-9]+(?<-bracket>\])(?(bracket)(?!)))?)(\.((_[a-zA-Z0-9]|[a-zA-Z])+((?<bracket>\[)[0-9]+(?<-bracket>\])(?(bracket)(?!)))?))*$

But I want to know if there is a better way without copying the original part.

Background:

I need to access a Micrologix 5000 machine that uses addressing. In a C # application, I want to validate that the user is entering a good address.

Allowed:

  • Dog.Tail

  • Dogs[0].Tail.IsMoving

Is not allowed:

  • Dog.

  • Dogs[0].

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1 answer


You can use recursion. See this:

^((_[a-zA-Z0-9]|[a-zA-Z])+((?<bracket>\[)[0-9]+(?<-bracket>\])(?(bracket)(?!)))?)(\.\1)*$
                                                                                    ^^


  • \1

    recurses the first submatrix in the first capture group ( )

    .

However, this is two steps less efficient than your programmed regex, which is optimal for this case. Recursion can be used here to improve readability, but is not recommended.

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