Creating an error message for an invalid input - ruby

Question

I have the following code that returns the # of days in any given month, which works fine unless someone types in something that isn't a date, or they format the date wrong. To remedy this I want to send out an error message for an invalid input, but I don't know how. So how do I create an error message for this small app?
#type in the month and year you want like so ---> "Feb 2034"
require 'date'
input = gets.chomp
inputArray = input.split(" ").to_a
textMonth = inputArray[0]
textYear = inputArray[1]
startOfMonth = Date.strptime(input, "%b %Y")
nextMonth = startOfMonth.next_month
endOfMonth = nextMonth - 1
daysInMonth = (endOfMonth - startOfMonth + 1).to_i
puts "#{textMonth} of year #{textYear} has #{daysInMonth} days!"

Answer 1

Probably the best way to do this is putting your input in a while loop, prompting for a new answer every time the input isn't what you expected it to be.
To check the input you should use a Regexp. Here's an explanation
how to write a regexp to match a date.

Answer 2

For Creating a Custom Error refer below code:
Here I create and raise InvalidDateError for the wrong date input.
#type in the month and year you want like so ---> "Feb 2034"
class InvalidDateError < StandardError
end
require 'date'
require 'pry-byebug'
input = gets.chomp
inputArray = input.split(" ").to_a
textMonth = inputArray[0]
textYear = inputArray[1]
begin
startOfMonth = Date.strptime(input, "%b %Y")
nextMonth = startOfMonth.next_month
endOfMonth = nextMonth - 1
daysInMonth = (endOfMonth - startOfMonth + 1).to_i
puts "#{textMonth} of year #{textYear} has #{daysInMonth} days!"
rescue StandardError=> e
raise InvalidDateError.new("Invalid Date : #{input}")
end
If you don't want to raise an error and only want to show error message then replace raise InvalidDateError.new("Invalid Date : #{input}")
with puts "Invalid Date : #{input}"

Answer 3

As suggested by Viktor, and stolen :) from crantok
require 'date'
date_valid = false
while !date_valid
puts 'Insert date as yyyy-mm-dd:'
input_date = gets.chomp
begin
parsed_date = Date.parse(input_date)
date_valid = true
rescue ArgumentError
puts 'format error'
end
end
month = parsed_date.month
year = parsed_date.year
days_in_month = Date.new(year, month, -1).day
puts "In #{year} month #{month} has #{days_in_month} days"