I have been attempting to validate a string in VB.net that must contain these three letters in no particular order and do not need to be next to One another. ABC
I can do this easily using LINQ
MessageBox.Show(("ABC").All(Function(n) ("AAAABBBBBCCCC").Contains(n)).ToString)
However, after searching Google and SO for over a week, I am completely stumped. My closest pattern is ".*[A|B|C]+.*[A|B|C]+.*[A|B|C]+.*" how ever AAA would also return true. I know i can do this using other methods just after trying for a week i really want to know if its possible using One regular expression.
Your original pattern won't work because it will match any number of characters, followed by one or more A, B, C, or | character, followed by any number of characters, followed by one or more A, B, C, or | character, followed by any number of characters, followed by one or more A, B, C, or | character, followed by any number of characters.
I'd probably go with the code you've already written, but if you really want to use a regular expression, you can use a series of lookahead assertions, like this:
(?=.*A)(?=.*B)(?=.*C)
This will match any string that contains A, B, and C in any order.
You can make use of positive lookaheads:
^(?=.*A)(?=.*B)(?=.*C).+
(?=.*A) makes sure there's an A somewhere in the string and the same logic applies to the other lookaheads.
You can use zero-width lookaheads. Lookaheads are great to eliminate match possibilities if they don't meet a certain criteria.
For example, let's use the words
untie queue unique block unity
Start with a basic word match:
\b\w+\b
to require the word matched with \w+ begins with un, we could use a positive lookahead
\b(?=un)\w+\b
What this says is
\b Match a blank(?=un) Are there the letters "un"? If not, NO MATCH. If so, then possible match.\w+ One or more word characters\b Match a blank
A positive lookahead eliminates a match possibility if it does NOT meet the expression inside. It applies to the regex RIGHT AFTER it. So the (?=un) applies to the \w+ expression above and requires that it BEGINS WITH un. If it does not, then the \w+ expression won't match.
How about matching any words that do not begin with un? Simply use a "negative lookahead"
\b(?!un)\w+\b
\b Match a blank(?!un) Are there the letters "un"? If SO, NO MATCH. If not, then possible match.\w+ One or more word characters\b Match a blank
So for your requirement of having at least 1 A, 1 B and 1 C in the string, a pattern like
(?=.*A)(?=.*B)(?=.*C).+
Works because it says:
(?=.*A) - Does it have .* any characters followed by A? If so, possible match if not no match.(?=.*B) - Does it have .* any characters followed by B? If so, possible match if not no match.(?=.*C) - Does it have .* any characters followed by C? If so, possible match if not no match..+ If the above 3 lookahead requirements were met, match any characters. If not, then match no characters (and so there isn't a match)
Does it have to be a regex? That's something that can easily be solved without one.
I've never programmed in VB, but I'm sure there are helper functions that let you take a string, and query whether or not a character occurs in it.
If str is your string, maybe something like:
str.contains('A') && str.contains('B') && str.contains('C')
