A regular expression matches any sentence, but avoids the repetition of characters

Question

I am looking for help to create a regex for checking a string that satisfies these 4 criteria:

• The string must contain a space.
• The line should end with a full stop / period.
• The string must contain at least 15 characters.
• The string must not contain a repetition of 3 or more characters. This is the part that I am especially struggling with.

For instance:

Pass

• One two three four.

Renouncement

• OOOne two thee four.
• Two of your affairs.
• One two three four
• Two three.
• Onetwothreefour.

If possible, could you explain how the regex is built to give me a better idea of ​​how to build them in the future?

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Here is what I have tried so far,

^(.*?={15,})(\.\Z)$ 

but I’m afraid that it won’t even close, please help.

Answer 1

You can use this regex:

 ^(?=\S*\s)(?!.*?(.)\1{2}).{14,}\.$ 

RegEx Demo

Explanation:

• (?=\S*\s) - Lookahead to make sure there are at least one spaces.
• (?!.*?(.)\1{2}) - Negative Lookahead to make sure there is no case with three consecutive characters.
• .{14,} to make sure there are at least 14 characters (the 15th last dot)
• \.$ to make sure the dot is always the last character