Regex - Does not contain certain Characters

👋 Hey there tech enthusiasts! Welcome to my super cool tech blog! Today, we're diving into the wonderful world of regular expressions, focusing on a common issue many of you face - how to find strings that DO NOT contain certain characters. 🚫

So, imagine you have a sentence and you want to check if it doesn't contain either the '<' or '>' characters. 😮 Our reader here was on the right track, but had a slight hiccup when it came to matching '<' or '>' that were not at the beginning or end of the string. Let's walk through a couple of easy solutions to this problem! 💪

One method is to use the negative lookahead assertion (?!...) in combination with a character class [...]. The negative lookahead (?!...) allows us to assert that a certain pattern does not follow our current position. In our case, we can assert that neither "<" nor ">" follows by using (?![<>]). This is because inside a character class, the negation operator ^ is not needed. 🙅‍♀️

To match anywhere in the sentence, our reader was really close! The dot . matches any character except a newline, and the asterisk * means to match the previous token (the dot in this case) zero or more times. By incorporating the negative lookahead into the regex, we can update it to:

^(?!.*[<>]).*$

Let's break it down:

• ^ asserts the beginning of the string.

• (?!.*[<>]) is the negative lookahead assertion to check if there are no occurrences of "<" or ">" anywhere in the string.

• .* matches any character zero or more times.

• $ asserts the end of the string.

Our regex pattern is locked and loaded, but we're not done yet! Our reader mentioned they were using .Net. Well, great news! Regex patterns are supported across various programming languages and tools, including .Net. So, no worries there! 🎉

Now that we've solved this common regex problem, it's your turn to give it a try! Take our regex pattern (?!.*[<>]).*$ and use it in your code to find those strings that don't contain "<" or ">". Then, you can share your awesome experience with us and let us know how it helped you! 💬

Remember, regular expressions can be a bit tricky at first, but with practice and a positive mindset, you'll become a regex master in no time! Keep exploring, keep learning, and keep rocking the tech world! 🌟

That wraps up today's blog post! If you found it helpful, don't forget to hit that share button and spread the regex love! Stay tuned for more fun and informative tech content. Until then, happy coding! 🤓👩‍💻