# IP Address

**URL:** <https://www.ruby-forum.com/t/ip-address/159599>\
**Category:** Rails\
**Created:** [February 6, 2009, 7:32am UTC](https://www.ruby-forum.com/t/ip-address/159599 "2009-02-06T07:32:49Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![newb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/2acd7d/32.png) [@newb](https://www.ruby-forum.com/u/newb)\
**Post date:** [February 6, 2009, 7:32am UTC](https://www.ruby-forum.com/t/ip-address/159599/1 "2009-02-06T07:32:49Z")

</div>

Hi…

I want to check for correct ip address while i submit the form.  
When i used below regular expression.it accepts 0.0.0.0 as ip address  
value.  
REGEXP\_HOST\_ADDRESS  
=/\A(?:25[0-5]|(?:2[0-4]|1\d|[1-9])?\d)(?:.(?:25[0-5]|(?:2[0-4]|1\d|[1-9])?\d)){3}\z/.  
But in my case it’s not a valid ip address.

so Pls help me with your assistance

---

<div class="post-metadata">

**Author:** ![newb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/2acd7d/32.png) [@newb](https://www.ruby-forum.com/u/newb)\
**Post date:** [February 6, 2009, 3:38pm UTC](https://www.ruby-forum.com/t/ip-address/159599/2 "2009-02-06T15:38:05Z")

</div>

There’s a good write-up here:

> **[Example: Matching Numeric Ranges with a Regular Expression](https://www.regular-expressions.info/numericranges.html)**
>
> Detailed example of building a regex to match a number in a given range of numbers

While not specific to matching an IP address, it does cover how to match  
ranges like 0-255.

Regards,  
Craig

---

<div class="post-metadata">

**Author:** ![newb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/2acd7d/32.png) [@newb](https://www.ruby-forum.com/u/newb)\
**Post date:** [February 6, 2009, 4:20pm UTC](https://www.ruby-forum.com/t/ip-address/159599/3 "2009-02-06T16:20:25Z")

</div>

Newb N. wrote:

> so Pls help me with your assistance

I’d try breaking it up a bit, and resolving this in stages.

It looks like you’re searching for string start, expr.expr.expr.expr,  
string end. The expr seems to be the same for each part, so if you solve  
it once then you can use it multiple times.

The (?🙂 creates a grouping without back references, which shouldn’t  
change the matching pattern, so I’ll ignore it for now. This makes your  
base expression

(25[0-5]|(2[0-4]|1\d|[1-9])?\d)

I think your problem is operator precedence and grouping. I’ll put in  
some more parentheses and some text to indicate how this expression is  
being parsed:

( (25[0-5]) or ( maybe one of these ( (2[0-4]) or (1(any digit)) or  
(1-9) ) and regardless then one of any digit ) )

broken down even further:

(one of 250,251,252,253,254,255)  
or  
( ( ( one of 20,21,22,23,24 or one of 10,11,12,13,14,15,16,17,18,19 or  
one of 1,2,3,4,5,6,7,8,9) or nothing) and 0,1,2,3,4,5,6,7,8,9)

put together, it looks like this matches everything from 0 to 255, which  
means 0.0.0.0 will match when you put 4 in a row. This may be more what  
you’re looking for:

([1-9]|1\d\d?|2[0-4]\d|25[0-5])

which matches (1 to 9) or (10 to 199) or (200-249) or (250-255). If you  
want to include 0 simply change the initial [1-9] to \d. E.g. matching  
any IP that doesn’t start with “0.” would be:

REGEXP\_HOST\_ADDRESS =  
/\A(?:[1-9]|1\d\d?|2[0-4]\d|25[0-5])(?:.(?:\d|1\d\d?|2[0-4]\d|25[0-5])){3}\Z/

```
-Chris
```