C# Regex - Match expression that does not start with a specific word

Question

I have read similar questions but I can't get this to work. I want to use the regex for the Find-Replace Visual Studio tool that supports C# regular expressions.

I want to find (and replace with nothing) expressions such as:

System.Collections.Generic.List
System.Web.UI.WebControls.Button

And remove System.Collections.Generic. and System.Web.UI.WebControls to tidy my code up.

BUT I want the ability to add new words after 'System.' to the expression if I want to scale it. So I have created this:

(System\\.)?(Collections\\.)?(Generic\\.)?(Web\\.)?(UI\\.)?(WebControls\\.)?

However, this also changes using statements such as:

using System.Data.SqlClient;

Is there a way to alter my regular expression so that it does not include matches that start with the "using" keyword?

I have tried using:

(^?!using)(System\\.)?(Collections\\.)?(Generic\\.)?(Web\\.)?(UI\\.)?(WebControls\\.)?

but this does not work. Thanks!

Answer 1

using negative lookbehind, to assert match is not preceeded by using

(?<!^using )

However as all parts are optionnal it will match Collections. in

using System.Collection.Generic.List

Which may be not wanted, also many regex engine have a limitation lookbehinds can't have a variable length match.

Answer 2

The syntax you have will allow for partial matching. Try specifying that "using" must appear 0 times. ^(using){0}

If that doesn't work, you can do the following: 1.Find and replace "using system" with "usingsistem". 2. Find and replace system.whatever. 3. Find and replace "usingsistem" with "using system"