Regex: I want this AND that AND that... in any order

You can use (?=…) positive lookahead; it asserts that a given pattern can be matched. You'd anchor at the beginning of the string, and one by one, in any order, look for a match of each of your patterns.

It'll look something like this:

^(?=.*one)(?=.*two)(?=.*three).*$

This will match a string that contains "one", "two", "three", in any order (as seen on rubular.com).

Depending on the context, you may want to anchor on \A and \Z, and use single-line mode so the dot matches everything.

This is not the most efficient solution to the problem. The best solution would be to parse out the words in your input and putting it into an efficient set representation, etc.

Related questions

• How does the regular expression (?<=#)[^#]+(?=#) work?

More practical example: password validation

Let's say that we want our password to:

• Contain between 8 and 15 characters
• Must contain an uppercase letter
• Must contain a lowercase letter
• Must contain a digit
• Must contain one of special symbols

Then we can write a regex like this:

^(?=.{8,15}$)(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])(?=.*[!@#$%^&*]).*$
 \__________/\_________/\_________/\_________/\______________/
    length      upper      lower      digit        symbol

Why not just do a simple check for the text since order doesn't matter?

string test = "NS306 FEBRUARY 20078/9/201013B1-9-1Low31 AUGUST 19870";
test = test.ToUpper();
bool match = ((test.IndexOf("FEB") >= 0) && (test.IndexOf("LOW") >= 0));

Do you need it to use regex?

I think the most expedient thing for today will be to string.Split(' ') the search terms and then iterate over the results confirming that sourceString.Contains(searchTerm)

var source = @"NS306 FEBRUARY 20078/9/201013B1-9-1Low31 AUGUST 19870".ToLowerInvariant();
var search = "FEB Low";

var terms = search.Split(' ');

bool all_match = !terms.Any(term => !(source.Contains(term.ToLowerInvariant())));

Notice that we use Any() to set up a short-circuit, so if the first term fails to match, we skip checking the second, third, and so forth.

This is not a great use case for RegEx. The string manipulation necessary to take an arbitrary number of search strings and convert that into a pattern almost certainly negates the performance benefit of matching the pattern with the RegEx engine, though this may vary depending on what you're matching against.

You've indicated in some comments that you want to avoid a loop, but RegEx is not a one-pass solution. It is not hard to create horrifically non-performant searches that loop and step character by character, such as the infamous catastrophic backtracking, where a very simple match takes thousands of steps to return false.