How to Check Whether a Value in a String Is an Ip Address

How do I check whether a value in a string is an IP address

Why not let a library validate it for you? You shouldn't introduce complex regular expressions that are impossible to maintain.

% gem install ipaddress

Then, in your application

require "ipaddress"

IPAddress.valid? "192.128.0.12"
#=> true

IPAddress.valid? "192.128.0.260"
#=> false

# Validate IPv6 addresses without additional work.
IPAddress.valid? "ff02::1"
#=> true

IPAddress.valid? "ff02::ff::1"
#=> false


IPAddress.valid_ipv4? "192.128.0.12"
#=> true

IPAddress.valid_ipv6? "192.128.0.12"
#=> false

You can also use Ruby's built-in IPAddr class, but it doesn't lend itself very well for validation.

Of course, if the IP address is supplied to you by the application server or framework, there is no reason to validate at all. Simply use the information that is given to you, and handle any exceptions gracefully.

check if a string matches an IP address pattern in python?

update: The original answer bellow is good for 2011, but since 2012, one is likely better using Python's ipaddress stdlib module - besides checking IP validity for IPv4 and IPv6, it can do a lot of other things as well.</update>

It looks like you are trying to validate IP addresses. A regular expression is probably not the best tool for this.

If you want to accept all valid IP addresses (including some addresses that you probably didn't even know were valid) then you can use IPy (Source):

from IPy import IP
IP('127.0.0.1')

If the IP address is invalid it will throw an exception.

Or you could use socket (Source):

import socket
try:
    socket.inet_aton(addr)
    # legal
except socket.error:
    # Not legal

If you really want to only match IPv4 with 4 decimal parts then you can split on dot and test that each part is an integer between 0 and 255.

def validate_ip(s):
    a = s.split('.')
    if len(a) != 4:
        return False
    for x in a:
        if not x.isdigit():
            return False
        i = int(x)
        if i < 0 or i > 255:
            return False
    return True

Note that your regular expression doesn't do this extra check. It would accept 999.999.999.999 as a valid address.

Validate whether a string is valid for IP Address or not

You can pretty straightforward check it: split string to parts separated by dot and ensure it will be exactly four parts having values in range 1...255:

string s = "123.123.123.123";

var parts = s.Split('.');

bool isValid = parts.Length == 4
               && !parts.Any(
                   x =>
                   {
                       int y;
                       return Int32.TryParse(x, out y) && y > 255 || y < 1;
                   });

Checking if a String Contains an IP

Mastering Regular Expressions (Third Edition) gives a pattern that will validate an IPv4 address, having four dot-separated integers in the range 0-255:

^(?:[01]?\d\d?|2[0-4]\d|25[0-5])\.
(?:[01]?\d\d?|2[0-4]\d|25[0-5])\.
(?:[01]?\d\d?|2[0-4]\d|25[0-5])\.
(?:[01]?\d\d?|2[0-4]\d|25[0-5])$

Modifying that to find (rather than validate) an IP, to exclude things that look like IPs turning up within longer strings of dotted digits, and escape backslashes for Java string syntax, we can render it in a Java method as:

public static String extractIP(String s) {
    java.util.regex.Matcher m = java.util.regex.Pattern.compile(
        "(?<!\\d|\\d\\.)" +
        "(?:[01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
        "(?:[01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
        "(?:[01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
        "(?:[01]?\\d\\d?|2[0-4]\\d|25[0-5])" +
        "(?!\\d|\\.\\d)").matcher(s);
    return m.find() ? m.group() : null;
}

That will return the IP if one is found in the string, or null otherwise.

To check simply if it contains an IP, do if (extractIP(str) != null) ....

How can I check if a String is an IP in Groovy?

You can use InetAddressValidator class to check and validate weather a string is a valid ip or not.

import org.codehaus.groovy.grails.validation.routines.InetAddressValidator

...
String someIp = // some String
if(InetAddressValidator.getInstance().isValidInet4Address(someIp)){
    println "Valid Ip"
} else {
    println "Invalid Ip"
}
...

Try this..,.

How can I simply validate whether a string is a valid IP in PHP?

$valid = ip2long($ip) !== false;

Advice/help/better solution for checking whether a given string can be a valid IP address or not

I found this question on the code review site. Since the code doesn't work as expected the question doesn't fit on code review, so I will provide the review here instead.

Magic Numbers

This was mentioned in a previous answer:

It is not clear in the code what the numbers 47, 48, 59 and 156 mean.

You can't assume that the character set in use is ASCII, therefore it is safer to use a range check based on 0 to 9.

   if(inputString[i] == '0' || inputString[i] == '.')
   {
       if(inputString[i+1] < '0' && inputString[i+1] > '9')
       {
           return false;
       }
   }

It might be better to use the isdigit function provided by ctype.h

   if(inputString[i] == '0' || inputString[i] == '.')
   {
       if(!isdigit(inputString[i+1]))
       {
           return false;
       }
   }

Complexity

This code would be easier to read, write, and debug if the function were broken into smaller functions that had only one purpose. Each one of the inner loops or checks should be a function.

The art of programming is the art of breaking problems into smaller and smaller pieces until each piece is very easy to solve. There are programming principles such as the Single Responsibility Principle that describe this.

Use the C Library to Make the Checks easier

There are 2 functions that can convert strings to integers that would make checking for numbers above 255 easier. The first is atoi and the second is strtol, either of these functions will give you a number you can compare to 255.

Determine if a string is a valid IPv4 address in C

I asked a similar question for C++. You should be able to use a slightly modified (for C) version of what I came up with back then.

bool isValidIpAddress(char *ipAddress)
{
    struct sockaddr_in sa;
    int result = inet_pton(AF_INET, ipAddress, &(sa.sin_addr));
    return result != 0;
}

You'll need to #include <arpa/inet.h> to use the inet_pton() function.

Update based on comments to the question: If you want to know if a C-style string contains an IP address, then you should combine the two answers given so far. Use a regular expression to find patterns that roughly match an IP address, then use the function above to check the match to see if it's the real deal.

Check if a string is a hostname or an ip-address in Java

While you could theoretically write rules to handle these cases yourself, using the usual cadre of RFCs, I'd instead look at the entirety of this class in Google Guava, especially the corner cases, such as how it resolves the embedding of 4-in-6 addresses.

As for determining if you have a FQDN, see if coercion to IP address fails, then try to resolve it against DNS. Anything else should, given your input cases, be a hostname or local resolution that isn't fully qualified.

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