正则表达式匹配以某个字符结尾但不以另一个以中间空格开头的字符串

Question

I am attempting to use the regex: (?<!:)[\\s]+" to no effect.

What I want is to match a quote mark preceded by whitespace UNLESS the whitespace is preceded by a colon.

The above regex is useless however as it matches incorrectly. The regex above will match the string :__" (using _ to represent a space) because it just matches _" . It starts matching at the second space, but it shouldn't match at all.

I'm looking for:

A " - MATCH
B " - MATCH
: " - NO MATCH
A:   " - NO MATCH
:    " - NO MATCH
:                           " - NO MATCH
:                A " - MATCH

The negative lookbehind doesn't help because it does match most of them.

Answer 1

One way to match the strings that you want is to require a character other than a space \\s or colon : to be present in front of \\s+ :

(?<![:\s])\s+"

Including space \\s in the list of negative look-behind ensures that a space cannot be counted as "not-a-colon" character for the purpose of matching a string.

Demo.

Answer 2

Try this

      const string FILENAME = @"\temp\test.txt";
        static void Main(string[] args)
        {
            string input = File.ReadAllText(FILENAME);
            string pattern = "^[^:]\\s+\"";

            MatchCollection matches = Regex.Matches(input, pattern, RegexOptions.Multiline);
        }​