Regular expression expression matching IP (recommended)

Here I will give you a detailed explanation of a regular expression that matches IP addresses.

Knowledge about regular expressions will be mentioned in the detailed explanation.

Before explaining, let me first introduce to you the rules for generating IP addresses.

The IP address is composed of a 32-digit binary number converted into a string of four decimal numbers.

How to convert? Explained below:

Binary: 111111111111111111111111111111

divided into four parts: 11111111.11111111.11111111.11111111

Conversion: 2^7+2^ 6+2^5+2^4+ 2^3+2^2+2^1+2^0=255

Convert to decimal range: 0~255.0~255.0~255.0~255

This is the range of the IP address.

Based on the rules and range of IP generation, we can use regular expressions to match the IP address, but how to match? Everyone has their own method, here I will explain my approach.

Based on the string rules of the IP address, I divided the expression matching the IP address into two parts to consider.

The first part: Match 3 0~255. (Note the dot at the end)

The second part: Match the last number 0~255

In other words, First match the string 0~255. (note the dot at the end), then repeat the match 3 times, and then match the last number part 0~255. This is my idea of ​​matching IP addresses.

First of all, I would like to mention that there is no way to do numerical operations with regular expressions, so we cannot use numerical operations to filter out the numerical range of IP. Since there is no way to filter out the numerical range of IP using number operations, what other methods should we use to filter this numerical range? My idea is to discuss in groups, and then merge these groups to form a numerical range of IP.

① Assuming that the IP number is in the hundreds digit, then based on the IP number range, we can draw the following situations. Assuming that the first number is 1, then the range of this number is 1[0-9][0-9]. This should not be difficult to understand, so I won’t explain it.

②. Assuming that the first number is 2, then according to the range rules of IP numbers, there are two situations here. Why? Think about it, the maximum number is 255. When the tens digit is 5, the single digit can only be 5 at most, right? And when the tens digit is 0 to 4, the ones digit can be any number, right?

So, the two situations here are:

A, 2[0-4][0-9]

B, 25[0-5]

③. After analyzing the hundreds digit situation, the next step is the tens digit situation. If it is a tens digit, then the first number in front of the tens digit cannot be zero, right?

So the ten-digit situation can be: [1-9][0-9]

④. The rest is the single-digit situation. The single-digit situation, Everyone should easily come to the conclusion, which is: [0-9].

After analyzing the four situations, we came to the conclusion that the range grouping of IP numbers is:

　　　1[0-9][0-9]

　　　2[0- 4][0-9]

25[0-5]

## How to express the above grouping using regular expressions? It's very simple, just use the regular or symbol | and the grouping symbol (), so the above grouping regular expression is:

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

At this point, the matching range regular expression for numbers has been written. So according to my previous ideas: The first part: Match 3 0~255. (note the dot at the end)

The second part: Match the last number 0~255

Let’s match The first part of the IP address, the regular expression is as follows:

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

I added a dot after each number to match 0~255. (Pay attention to the dot at the end)

Then How to repeat the match three times? It's very simple. We just need to treat these five groups as a whole and repeat the matching three times. The regular expression is as follows:

((1[0-9][0-9]\.)|(2[0-4][0-9]\.)|(25[0-5]\.)|([1-9][0-9]\.)|([0-9])\.)){3}

The first part has been matched. The next step is to splice the numbers in the second part. , the numerical part has been written very clearly above, so I won’t explain it anymore. The following is the complete regular expression:

((1[0-9][0-9]\.)|(2[0-4][0-9]\.)|(25[0-5]\.)|([1-9][0-9]\.)|([0-9]\.)){3}((1[0-9][0-9])|(2[0-4][0-9])|(25[0-5])|([1-9][0-9])|([0-9]))

   　　 写到这里，正则匹配IP的表达式已经出来了，不过，这并不是最终的匹配IP的正则表达式，为什么呢？很简单，正则表达式会对每一个分组都进行捕获匹配，上面把匹配IP分成了那么多分组，而每一个分组的内容都会被正则所捕获，那上面不知道已经捕获多少IP了，呵呵，那么怎么去掉分组的内容呢？很简单，用这个符号?:

　　    ?:符号放在()圆括号里面，是捕获分组，但不捕获正则表达式的内容的意思。那么，我们把它放到每一个分组里面去，不就去掉了分组的内容了吗？所以，我们还要给每个分组加上?:，加上后正则如下：

(?:(?:1[0-9][0-9]\.)|(?:2[0-4][0-9]\.)|(?:25[0-5]\.)|(?:[1-9][0-9]\.)|(?:[0-9]\.)){3}(?:(?:1[0-9][0-9])|(?:2[0-4][0-9])|(?:25[0-5])|(?:[1-9][0-9])|(?:[0-9]))

　　  即使到这里，还是没有把IP地址匹配出来，我们还要用^和$来限制字符串的开头和结尾，所以，最后的匹配IP地址的正则表达式是：

^(?:(?:1[0-9][0-9]\.)|(?:2[0-4][0-9]\.)|(?:25[0-5]\.)|(?:[1-9][0-9]\.)|(?:[0-9]\.)){3}(?:(?:1[0-9][0-9])|(?:2[0-4][0-9])|(?:25[0-5])|(?:[1-9][0-9])|(?:[0-9]))$

   

　　  这就是我匹配IP地址最完整的正则表达式，大家可以借鉴一下，有什么bug还望读者提出，免得误导其他读者。

　　　 上面的正则表达式的()括号都是成对出现的，假如有不成对出现，请读者自己添加一下，可能是我漏写了。

　　　 下面是我的测试：

<?php
$pattern = &#39;/^(?:(?:2[0-4][0-9]\.)|(?:25[0-5]\.)|(?:1[0-9][0-9]\.)|(?:[1-9][0-9]\.)|(?:[0-9]\.)){3}(?:(?:2[0-5][0-5])|(?:25[0-5])|(?:1[0-9][0-9])|(?:[1-9][0-9])|(?:[0-9]))$/&#39;;
//正则匹配ip地址
$ip     = &#39;254.21.0.198&#39;;
preg_match($pattern,$ip,$out);
echo &#39;<pre class="brush:php;toolbar:false">&#39;;
print_r($out);
$ip     = &#39;255.777.0.198&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;07.25.8.198&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;1207.25.8.198&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;qq107.25.8.198&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;\.\.\.107.25.8.198&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;\.\.\.  7.25.8.198&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;107.25.8.19822vvv&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;107.25.r8.1982&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;107.225.8.19&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;225.225.225.225&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;0.0.0.0&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;00.0.0.0&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;0.202.1.0&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;0.202.1.226&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$ip     = &#39;249.202.1.0&#39;;
preg_match($pattern,$ip,$out);
print_r($out);
$s=&#39;&#39;;
for($i=0;$i<32;$i++){
  $s .= &#39;1&#39;;
}
echo $s;
echo strlen($s);

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