Regular expression to validate IPv4 address in ruby

Question

I want to verify whether a given string is valid IPv4 address or not in ruby. I tried as follows but what is does is matches values greater than 255 as well. How to limit each block's range from 0-255

str="255.255.255.256"
if str=~ /\b[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\b/
puts true
else
puts false
end

Or if you really want to stick with regexp solutions: http://stackoverflow.com/questions/106179/regular-expression-to-match-hostname-or-ip-address — samuil, Apr 17 '14 at 06:34

score 15 · Answer 1 · edited Apr 17 '14 at 07:42

15

You have the IPAddr class in Ruby. You do not need to validate it agains a regex, just create a new object and catch the exception when it fails:

require 'ipaddr'

ip = IPAddr.new "127.0.0.1"
# => #<IPAddr: IPv4:127.0.0.1/255.255.255.255>

ip = IPAddr.new "127.0.0.a"
# => IPAddr::InvalidAddressError: invalid address

edited Apr 17 '14 at 07:42

sawa

165,429
45
277
381

answered Apr 17 '14 at 07:13

Paulo Fidalgo

21,709
7
99
115

2

Actually just catching this exception is not enough to ensure you have an IPv4 address, you also need to check `ip.ipv4?` returns `true`. Consider the example given in the docs: `IPAddr.new "3ffe:505:2::1"`. This does not raise an exception, as it is a valid IPv6 address. – MatzFan Dec 11 '17 at 13:27

sawa · Accepted Answer · 2016-01-20T18:44:11.267

9

block = /\d{,2}|1\d{2}|2[0-4]\d|25[0-5]/
re = /\A#{block}\.#{block}\.#{block}\.#{block}\z/

re =~ "255.255.255.255" # => 0
re =~ "255.255.255.256" # => nil

edited Jan 20 '16 at 18:44

answered Apr 17 '14 at 06:36

sawa

165,429
45
277
381

1

Thanks a lot @sawa. Your answer helped me understand regex in a much better way. Finally i created a new regex on my own. – Aniket Apr 17 '14 at 09:25
Why are you changing the regex? Yours is wrong; it does not accept `"199"` as a block. Also, explicitly returning a boolean value is a bad idea. If you want to convert the result into a boolean, do `!!` to the result. – sawa Apr 17 '14 at 09:29
yes, i was wrong, thnx again. – Aniket Apr 17 '14 at 09:31
1

Does not work :( - re =~ '192.168.0.74' => nil – Roman Gaufman Jan 20 '16 at 18:32
@RomanGaufman Thanks, I fixed it. – sawa Jan 20 '16 at 18:44
There is a Problem with Ruby 2.5.1 ```> re =~ ".255.255.255" => 0``` it returs 0, but it shouldn't – user2699706 Sep 17 '18 at 12:15

score 7 · Answer 3 · edited May 23 '17 at 11:46

7

You'd better to use ruby core class IPAddress

you could do it this way:

 require "ipaddress"

 IPAddress.valid? "192.128.0.12"
 #=> true

 IPAddress.valid? "192.128.0.260"
 #=> false

you could find more here How do I check whether a value in a string is an IP address

edited May 23 '17 at 11:46

Community

1
1

answered Apr 17 '14 at 06:55

shemerey

501
2
5

I don't want to use inbuilt function. – Aniket Apr 17 '14 at 07:38
6

Actually [ipaddress](https://rubygems.org/gems/ipaddress) is a gem, not a core class. – toro2k Apr 17 '14 at 07:57

score 1 · Answer 4 · answered Apr 17 '14 at 07:10

1

This is a way that reads pretty easily:

str.count('.')==3 && str.split('.').all? {|s| s[/^\d{3}$/] && s.to_i < 256}

answered Apr 17 '14 at 07:10

Cary Swoveland

106,649
6
63
100

Regular expression to validate IPv4 address in ruby

4 Answers4