Regex to allow letters, one space between words and a total length of 50

Question

I'm trying to build a regular expression with the following conditions:

• Only letters
• One space between words (no more than one space)
• Maximum length 50

And this is what I have done so far:

^(([A-Za-z]+( [A-Za-z])+){1,50})$

This allows me to validate the spaces between words and only letters conditions but it is not working for the length and it's not working for words without spaces, example:hello. Can someone help me with this?

Example:

What I need: Regex that allows sentences (with max length 50) like this:

Hello this is an example
Hello
a b c

Answer 1

Try this:

^\b(?!.*?\s{2})[A-Za-z ]{1,50}\b$

Demo

[A-Za-z ]{1,50} will check for the characters and length, while the negative lookahead (?!.*?\s{2}) will check for the spaces condition. (\b) to disallow white space at ends.