RegEx for String.Format

Question

Hiho everyone! :)

I have an application, in which the user can insert a string into a textbox, which will be used for a String.Format output later. So the user's input must have a certain format:

I would like to replace exactly one placeholder, so the string should be of a form like this: "Text{0}Text". So it has to contain at least one '{0}', but no other statement between curly braces, for example no {1}.

For the text before and after the '{0}', I would allow any characters.

So I think, I have to respect the following restrictions: { must be written as {{, } must be written as }}, " must be written as \" and \ must be written as \.

Can somebody tell me, how I can write such a RegEx? In particular, can I do something like 'any character WITHOUT' to exclude the four characters ( {, }, " and \ ) above instead of listing every allowed character?

Many thanks!! Nikki:)

Answer 1

It sounds like you're looking for the [^CHARS_GO_HERE] construct. The exact regex you'd need depends on your regex engine, but it would resemble [^({})].

Check out the "Negated Character Classes" section of the Character Class page at Regular-Expressions.info.

Answer 2

[^(){}\r\n]+\{0}[^(){}\r\n]+

will match any text except (, ), {, } and linebreaks, then match {0}, then the same as before. There needs to be at least one character before and after the {0}; if you don't want that, replace + with *.

You might also want to anchor the regex to beginning and end of your input string:

^[^(){}\r\n]+\{0}[^(){}\r\n]+$

Answer 3

(Similar to Tim's answer)

Something like:

^[^{}()]*(\{0})[^{}()]*$

Tested at http://www.regular-expressions.info/javascriptexample.html

Answer 4

I hate to be the guy who doesn't answer the question, but really it's poor usability to ask your user to format input to work with String.Format. Provide them with two input requests, so they enter the part before the {0} and the part after the {0}. Then you'll want to just concatenate the strings instead of use String.Format- using String.Format on user-supplied text is just a bad idea.

Answer 5

I think your question can be answered by the regexp:

^(((\{\{|\}\}|\\"|\\\\|[^\{\}\"\\])*(\{0\}))+(\{\{|\}\}|\\"|\\\\|[^\{\}\"\\])*$

Explanation:

The expression is built up as follows:

^(allowed chars {0})+(allowed chars)*$

one or more sequences of allowed chars followed by a {0} with optional allowed chars at the end.

allowed chars is built of the 4 sequences you mentioned (I assumed the \ escape is \\ instead of \.) plus all chars that do not contain the escapes chars:

(\{\{|\}\}|\\"|\\\\|[^\{\}\"\\])

combined they make up the regexp I started with.