Question

I’ve these three regular expressions. They work individually but i would like to merge them in a single pattern.

regex1 = [0-9]{16}
regex2 = [0-9]{4}[-][0-9]{4}[-][0-9]{4}[-][0-9]{4}
regex3 = [0-9]{4}[ ][0-9]{4}[ ][0-9]{4}[ ][0-9]{4}

I use this method:

Pattern.compile(regex);

Which is the regex string to merge them?

Answer 1

You can use backreferences:

[0-9]{4}([ -]|)([0-9]{4}\1){2}[0-9]{4}

This will only match if the seperators are either all

• spaces
• hyphens
• blank

\1 means “this matches exactly what the first capturing group – expression in parentheses – matched”.

Since ([ -]|) is that group, both other separators need to be the same for the pattern to match.

You can simplify it further to:

\d{4}([ -]|)(\d{4}\1){2}\d{4}