Replace single backslash with double backslash

c# regex string replace backslash
Johnny picture Johnny · May 24, 2011 · Viewed 36k times · Source

It seems simple enough, right? Well, I don't know.

Here's the code I'm trying:

input = Regex.Replace(input, "\\", "\\\\\\");

However, I'm receiving an error,

ArgumentException was unhandled - parsing "\" - Illegal \ at end of pattern.

How do I do this?

Answer

porges picture porges · May 24, 2011

The first one should be "\\\\", not "\\". It works like this:

  • You have written "\\".
  • This translates to the sequence \ in a string.
  • The regex engine then reads this, which translates as backslash which isn't escaping anything, so it throws an error.

With regex, it's much easier to use a "verbatim string". In this case the verbatim string would be @"\\". When using verbatim strings you only have to consider escaping for the regex engine, as backslashes are treated literally. The second string will also be @"\\", as it will not be interpreted by the regex engine.

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