6 digits regular expression

Question

I need a regular expression that requires at least ONE digits and SIX maximum.

I've worked out this, but neither of them seems to work.

^[0-9][0-9]\?[0-9]\?[0-9]\?[0-9]\?[0-9]\?$  ^[0-999999]$ 

Any other suggestion?

Answer 1

You can use range quantifier {min,max} to specify minimum of 1 digit and maximum of 6 digits as:

^[0-9]{1,6}$ 

Explanation:

^     : Start anchor [0-9] : Character class to match one of the 10 digits {1,6} : Range quantifier. Minimum 1 repetition and maximum 6. $     : End anchor 

Why did your regex not work ?

You were almost close on the regex:

^[0-9][0-9]\?[0-9]\?[0-9]\?[0-9]\?[0-9]\?$ 

Since you had escaped the ? by preceding it with the \, the ? was no more acting as a regex meta-character ( for 0 or 1 repetitions) but was being treated literally.

To fix it just remove the \ and you are there.

See it on rubular.

The quantifier based regex is shorter, more readable and can easily be extended to any number of digits.

Your second regex:

^[0-999999]$ 

is equivalent to:

^[0-9]$ 

which matches strings with exactly one digit. They are equivalent because a character class [aaaab] is same as [ab].