regular expression

Question

This regular expression /^(?:([A-Za-z])(?!\1))*S(?:([A-Za-z])(?!\1{2})){3,30}\ not working. Why?

I need a string:

• length between 3 and 30 - {3,30}
• no to repeating the first letter more than once - /^(?:([A-Za-z])(?!\1))
• no to the repetition of the same letter more than two consecutive times - /^(?:([A-Za-z])(?!\1{2}))
• after the first three letters there can be only one space

E.G.

• "iioy" no;
• "ioy" yes;
• "ioyy" yes;
• "ioyyytt" no;
• "ioy ycgu" yes;
• "ioy ycgu fdt" no;
• "ioy yycgu" no;

Answer 1

Look if it satisfies your requirements:

^(?:([A-Za-z])(?!\1))(?!.* .* )(?:([A-Za-z ])(?!\2{2})){2,29}$

Your reference to the second captured group was wrong: \1 instead of \2. Other than that I excluded spaces in the second negative lookahead. I also fixed the length since the quantifier doesn't apply to your first group.

You can test it here https://regex101.com/r/Y1AT1L/1