Regular expression to match A, AB, ABC, but not AC. (“starts with”)

by

Try this regular expression:

^(A(B(C)?)?)?$

I think you can see the pattern and expand it for ABCD and ABCDE like:

^(A(B(C(D)?)?)?)?$
^(A(B(C(D(E)?)?)?)?)?$

Now each part depends on the preceeding parts (B depends on A, C depends on B, etc.).

More Related Contents:

  1. Regex – To allow numeric, only characters R, N, X, B, @ [closed]
  2. Regex for Email Address along with name format [duplicate]
  3. Negative lookbehind equivalent in JavaScript
  4. JavaScript regex multiline text between two tags
  5. Case insensitive regex in JavaScript
  6. I want to remove double quotes from a String
  7. Replace a Regex capture group with uppercase in Javascript
  8. Regular Expression | Leap Years and More
  9. List of all characters that should be escaped before put in to RegEx?
  10. Matching exact string with JavaScript
  11. Match any non-word character (excluding diacritics)
  12. Finding Plus Sign in Regular Expression
  13. Combining regular expressions in Javascript
  14. Why does String.match( / \d*/ ) return an empty string?
  15. RegEx: How can I match all numbers greater than 49?
  16. How can I replace newlines/line breaks with spaces in javascript?
  17. How do I split a string by whitespace and ignoring leading and trailing whitespace into an array of words using a regular expression?
  18. Remove specific HTML tag with its content from javascript string
  19. In a regular expression, match one thing or another, or both
  20. Regex only capturing last instance of capture group in match
  21. (*SKIP)(*FAIL) workaround in JavaScript RegExp
  22. What is the need for caret (^) and dollar symbol ($) in regular expression?
  23. Javascript RegExp for splitting text into sentences and keeping the delimiter
  24. Commenting Regular Expressions
  25. How to insert space every 4 characters for IBAN registering?
  26. How can I use regex to get all the characters after a specific character, e.g. comma (“,”)
  27. What’s different between Python and Javascript regular expressions?
  28. Extract keyword from Google search in Javascript
  29. Regex matching emoticons
  30. Regex: only alphanumeric but not if this is pure numeric

Leave a Comment