regex expression to accept ENTER key in string

Question

Issue

I am having an issue creating a regex to accept any string and the ENTER key, at the moment i have this:

^$|^.+$

I have looked around and people have said to add \n but this does not work.

An example of the string is should allow is as follows:

Hello this is a test string


and i want this to be accepted

It seems you need `(?s)^.*$`. However, what good is this regex that matches all, incl. empty, strings? Could you please precise the requirements? — Wiktor Stribiżew, Jul 11 '16 at 14:32
Why do you need regex? More specifically, what are you trying to do that requires you to receive an enter key in a string using regex? Is it a console based app? You tagged the question c#, but there's no c# code or anything that relates to c# here. More to the point: are you looking for new lines in a string (that is, the enter key's representation in a series of characters), or to accept a string as input? — Richard Barker, Jul 11 '16 at 14:37
@WiktorStribiżew Basically its a C# windows service application where we want to handle validation through an engine in SQL. We are then able to change the Validation as we wish without doing a an update to the product. In a few weeks we will be tightening the validation on some things but for now we have it in place. — Ben Clarke, Jul 11 '16 at 14:42
So, is it just a matter of adding `RegexOptions.Singleline` flag to your regex? Like `new Regex(@"^.*$", RegexOptions.Singleline)`? — Wiktor Stribiżew, Jul 11 '16 at 14:44

wpcarro · Answer 1 · 2016-07-11T15:04:10.363

2

Try setting the s flag on the regex engine. This will ensure that the . metacharacter will match newlines.

Also, as a sidenote, instead of ^$|^.+$ you can condense the whole expression to ^.*$ to achieve the same results with better performance.

edited Jul 11 '16 at 15:04

answered Jul 11 '16 at 14:35

wpcarro

s is whitespace, not multiline – deltree Jul 11 '16 at 14:38
`\s` is whitespace. The `m` flag is multiline, but that's not what I'm referencing. The `s` flag is single-line mode, making `.` match newline characters. View the example if you're confused about the distinctions. – wpcarro Jul 11 '16 at 14:39

score 1 · Answer 2 · answered Jul 11 '16 at 14:49

In C#, you need the RegexOptions.Singleline option. See this SO post for more information.

Here is a quick example that really just matches the entire string, so it's not useful.

var regex = new Regex(@"^.*$",
              RegexOptions.IgnoreCase | RegexOptions.Singleline);

In your future validation code, you need to replace .* with whatever your validation will be.