I'm trying to limit the entries to a specific format.
If the entry has 5500 or 5100 such as 01\01-5500-000-00 then I want to have this:
^[0-9]{2,}\\[0-9]{2}\-[0-9]{4}\-[0-9]{3}\-$
But if the entry has anything other than 5500 or 5100 I want to have this:
^[0-9]{2,}\\[0-9]{2}\-[0-9]{4}\-[0-9]{3}\-[0-9]{2}$
How can this be accomplished with the if then else idea?
Conditional regex syntax is not supported by JavaScript regex engine, but it can be worked around with a non-capturing group containing 2 alternatives:
One with the positive look-ahead and
The second with the reversed, negative look-ahead.
This regex meets your criteria and is JavaScript compatible:
^(?:(?=.*\b5[15]00\b)[0-9]{2,}\\[0-9]{2}-[0-9]{4}-[0-9]{3}-|(?!.*\b5[15]00\b)[0-9]{2,}\\[0-9]{2}-[0-9]{4}-[0-9]{3}-[0-9]{2})$
See regex demo
Let me break it down:
^ - Start of string(?:
(?=.*\b5[15]00\b)[0-9]{2,}\\[0-9]{2}-[0-9]{4}-[0-9]{3}- - First alternative with the (?=.*\b5[15]00\b) look-ahead that requires a whole word 5500 or 5100 inside the string, and the first pattern you have| - alternation operator(?!.*\b5[15]00\b)[0-9]{2,}\\[0-9]{2}-[0-9]{4}-[0-9]{3}-[0-9]{2}) - Second alternative that is prepended with the (?!.*\b5[15]00\b) negative look-ahead that makes sure there is no 5100 or 5500 inside the string, and only then matches your second pattern.$ - end of string.
Use conditionals, Eg:
(?(?=regex)then|else): [0-9]{2,}\\[0-9]{2}\-(?(?=5[15]00)[0-9]{4}\-[0-9]{3}\-|[0-9]{4}\-[0-9]{3}\-[0-9]{2})
Regex conditionals example: [email protected]
In case that you're using a regex engine that is not PCRE based, you can be able to mimic the functionality by doing the following:
((?=positive-regex-statement)then|(?!negavite-regex-statement)then)
Eg.
^[0-9]{2,}\\[0-9]{2}\-((?=5[15]00)[0-9]{4}\-[0-9]{3}\-|[0-9]{4}\-|(?!5[15]00)[0-9]{4}\-[0-9]{3}\-[0-9]{2})$
Mimic regex conditionals example: [email protected]
Replace this part of the pattern [0-9]{4} with the literal values for 5100/5500:
/^\d{2,}\\\d{2}-(?:5[15]00-\d{3}-|(?!5[15]00)\d{4}-\d{3}-\d{2})$/
[0-9] is the same thing as \d in JavaScript(?!5[15]00)\d{4} to guarantee it's not 5100/5500.
^[0-9]{2,}\\[0-9]{2}-5[15]00-[0-9]{3}-$|^[0-9]{2,}\\[0-9]{2}-(?!5[15]00)[0-9]{4}-[0-9]{3}-[0-9]{2}$01\01-5500-000-00does not match your first pattern. is it supposed to fail? Also, is the trailing"-"in the first pattern intentional?