Match a string that does not contain a certain character sequence

Question

I'm trying to use regular expressions to match a string that does not contain the sequence of characters of a less than symbol (<) followed by a non space. Here are some examples

Valid - "A new description."
Valid - "A < new description."
Invalid - "A <new description."

I can't seem to find the right expression to get a match. I'm using the Microsoft Regular Expression validator, so I need it to be a match and not use code to negate the match.

Any assistance would be appreciated.

Thanks,
Dale

Answer 1

var reg = new Regex(@"<(?!\s)");
string text = "it <matches";
string text2 = "it< doesn't match";

reg.Match(text);// <-- Match.Sucess == true
reg.Match(text2);// <-- Match.Sucess == false

Answer 2

Use a negative look-ahead: "<(?! )"

Answer 3

Hi

I think this might be what your looking for.

Valid - "A new description."
Valid - "A < new description."
Invalid - "A <new description."



 Try this:   <\S

This looks for something that has a less then sign and has a space missing after it.

In this case it would match "<n"

Not sure how much it you want it to match though.

Answer 4

In other words, you allow two things in your string:

1. Any character EXCEPT a <
2. A < followed by a space.

We can write that quite directly as:

/([^<]|(< ))+/

Answer 5

@"^(?:[^<]+|<(?!\s))*$"

Doing a negative lookahead for space allows it to match if the last character in the string is "<". Here's another way:

^(?!.*<\S).+$

The lookahead scans the whole string for a "<" immediately followed by a non-whitespace character. If it doesn't find one, the ".+" goes ahead and matches the string.