Regex for series of four digits each up to 100

Question

I'm trying to write a regex to validate a string and accepts only a series of four comma-separated digits, each up to 100. Something like this would be valid:

20,30,40,50

and these invalid:

120,0,20,0
20,30,40,ss
invalid_string

Any thoughts?

They're used for CMYK colours. We just need to store them here, not use them.

Answer 1

Number Range and Subroutine

In Ruby 2+, for a compact regex, use this:

^([0-9]|[1-9][0-9]|100)(?:,\g<1>){3}$

Explanation

• The ^ anchor asserts that we are at the beginning of the string
• The parentheses around ([0-9]|[1-9][0-9]|100) match a number from 0 to 100 and define subroutine #1
• (?:,\g<1>) matches one comma and the expression defined by subroutine # 1
• The {3} quantifier repeats that three times
• The $ anchor asserts that we are at the end of the string

Answer 2

I'd save myself the headache of using regex for a number related problem. Also the validation message will look akward so it's better to make your own:

validate :that_string_has_only_4_numbers_upto_100

def that_string_has_only_4_numbers_upto_100
  errors.add(:str, 'is not valid.') unless str.split(/,/).all? { |n| 1..100 === n.to_i }
end

Unless you a re regex jedi guru like @zx81 :p.