Ruby programming: How to truncate IP address?

Question

For various purposes I find myself needing to truncate an IP address, I need to alter an IP address within my program from (xx.x.x.x) to (xx.x.x.1) by changing the last number after the final "." in the string to the value of 1.

I theorise that this could be achieved by either truncating the string from the very end up to the final ".", and adding a "1" onto the end of it, or somehow by ordering the program to alter the string value after the final "." to be equal to 1 - none of which i know how to do.

I have seen various tutorials on both truncating and altering strings in Ruby, however none seem to cover something quite as complicated.

In short, my question:

- How do i change the value of the last number after the final "." in my IP address to the value of 1 (using either aforementioned method in paragraph 2)?

- Will this require a variable class change from string to int etc?

Thank you in advance.

What have you tried? Also, why do you want a 1 at the end? A subnet is denoted with zero/es at the end. — John Dvorak, Oct 14 '15 at 12:54
I would use a regex, but finding the last index of a dot should also work, albeit less elegantly — John Dvorak, Oct 14 '15 at 12:57

score 1 · Answer 1 · answered Oct 14 '15 at 12:53

Ruby is an object-oriented language, not a string-oriented or integer-oriented language. You should use objects in your program, not strings or integers. (Unless your objects are strings or integers, of course. But an IP address is not a string or an integer, it's an IP address.)

Once you switch over to using IP addresses, your problem becomes trivial:

require 'ipaddr'

ip = IPAddr.new('12.34.56.78')

(ip & IPAddr.new(255.255.255.0)).succ
# => #<IPAddr: IPv4:12.34.56.1/255.255.255.255>

Ruby programming: How to truncate IP address?

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