Trying to build a regular expression to check pattern

Question

a) Start and end with a number
b) Hyphen should start and end with a number
c) Comma should start and end with a number
d) Range of number should be from 1-31

Answer 1

Here is my workings

Numbers:

0|([1-9][0-9]*) call this expression A Note this expression treats zero as a special case and prevents numbers starting with a zero eg 0000001234

Number or a range:

A|(A-A) call this expression B (i.e (0|([1-9][0-9]*))|((0|([1-9][0-9]*))-(0|([1-9][0-9]*)))

Comma operator

B(,B)*

Putting this togher should do the trick and we get

((0|([1-9][0-9]*))|((0|([1-9][0-9]*))-(0|([1-9][0-9]*))))(,((0|([1-9][0-9]*))|((0|([1-9][0-9]*))-(0|([1-9][0-9]*)))))*

You can abbreviatge this with \d for [0-9]