How do I remove all non alphanumeric characters from a string except dash?

Use a regular expression that matches everything except letters, digits, and dash, then replace those characters with an empty string. For example (in JavaScript):

const str = "Hello@World - Example!";
const cleaned = str.replace(/[^a-zA-Z0-9-]+/g, "");
console.log(cleaned); // "HelloWorld-Example"

• [^a-zA-Z0-9-] is a character class that matches any character not in the set [a-zA-Z0-9-].
• Adding + quantifier ([^...]+) matches one or more such characters in a row.
• The g flag applies the replacement to all occurrences.
• Everything except letters (a-z, A-Z), digits (0-9), and dash (-) is removed.

1. Details & Caveats

1. Placement of Dash in Bracket

   • In many regex engines, you can safely include - as the last or first character in your bracket class (e.g., [A-Za-z0-9-] or [-A-Za-z0-9]) without escaping.
   • If you want - inside the bracket among other characters, you often must escape it like \- (e.g., [A-Za-z0-9\-]) to avoid range interpretations.

2. Case Insensitivity

   • Here, [a-zA-Z0-9-] explicitly covers upper and lower case letters, so you don’t need a separate flag for case-insensitive matching.

3. Unicode / Accented Characters

   • If your string might contain accented letters or other Unicode characters, [a-zA-Z] might be too restrictive. You can consider something like [\p{L}\p{N}-] in regex flavors that support Unicode properties (PCRE, etc.). JavaScript’s u flag can help, but that’s more advanced.

4. Cross-Language Implementation

   • The concept is similar in Python, Java, Ruby, and others. For instance, in Python:

     import re
     
     s = "Hello@World - Example!"
     cleaned = re.sub(r'[^a-zA-Z0-9-]+', '', s)
     print(cleaned)  # HelloWorld-Example

2. Example Variations

1. If You Also Want to Keep Spaces

   const cleaned = str.replace(/[^a-zA-Z0-9-\s]+/g, "");
   // Adds \s (whitespace) to the "allowed" set

2. If You Allow Underscores (_)

   const cleaned = str.replace(/[^a-zA-Z0-9-_]+/g, "");
   // Keeps underscores as well

3. If You Only Remove Non-Alphanumerics (i.e., Keep Dashes + Everything Else)

   • Then you’d want to remove only specifically matched characters rather than everything but your set. (Or invert the logic, depending on your exact needs.)

Summary

• A negated character class [^a-zA-Z0-9-] is your go-to solution, removing everything that isn’t letters, digits, or dash.
• Adjust the pattern for additional allowed characters, such as spaces or underscores, by adding them to the bracket.
• This approach is language-agnostic—just use the appropriate regex and string-replacement function in your target environment.---

Bonus: Level Up Your Regex & Coding Skills

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1. Grokking JavaScript Fundamentals
   Dive deeper into closures, prototypes, async/await, and more—ideal for debugging or customizing complex regex tasks.

2. Grokking the Coding Interview: Patterns for Coding Questions
   Learn how to approach coding problems using pattern-based solutions—an invaluable skill for both interviews and day-to-day engineering.

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