PHP preg_match needed to ensure only ONE space character is allowed between words

Question

basically I need a preg_match that ensures that only one space character is allowed between each word (IF there is more than one word).

My existing rule is:

Answer 1

It depends what you mean by "word", but assuming you mean letters in A-Z or a-z you can try this:

^[a-zA-Z]+( [a-zA-Z]+)*$

Note that \s does not mean the space character - it means any whitespace, including a new line.