How can I use Regex to find if I used the same character in multiple different locations?

Question

So I am looking through different numbers that have different delimiters, and I want to find all numbers that have the same delimiter.

Basically, I want the following

123+456+7890 // MATCH
123-456-7890 // MATCH
123.456.7890 // MATCH
123+456-7890 // FAILURE

My current regex I plan to use was

\d{3}[+-.]\d{3}[+-.]\d{4}

However, it would match number sequences that have the different delimiters. I don't want to use one big huge OR for something like this because the real life equivalent has many more characters that could fit there.

Is there a way to match the same character in multiple locations?

Answer 1

You can use a captured group and a back-reference to ensure same delimiter is used again.

^\d{3}([+.-])\d{3}\1\d{4}$

• ([+.-]) here we capture delimiter in group #1
• \1 Here we are using back-reference of same delimiter

RegEx Demo

Answer 2

You can use a back reference like this:

\d{3}([+.-])\d{3}\1\d{4}

• The first operator that is matched [+-.] is kept inside a capturing group so that it can be referenced later.
• \1 is a backreference to the first capturing group which in this case is [+-.] so it will ensure that the operator is same as the previous one.

Regex 101 Demo

You can read more about backreferences here