How to use regular expressions to match legal IPv4 addresses

Methods to match legal IPv4 addresses using regular expressions: Use regular expression ^(([0-9]|1-9|1[0-9]{2}|20-4|25[0-5]).){3}([0-9]|1-9|1[0-9]{2}|20-4|25[0-5])$ to match four numbers, each paragraph 0-255, separated by dots.

Use regular expressions to match legal IPv4 addresses

method:

Use the following regular expression to match the IPv4 address:

 <code>^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$</code>

step:

1. Leading anchor (^): Make sure the string matches from the beginning.
2. Repeat part ((([0-9]|1-9|1[0-9]{2}|20-4|25[0-5]).)): Matches four numbers in an IPv4 address, separated by dots, and each number can take a value of 0-255.
3. Loop 3 times: This section is repeated 3 times to match the four numeric fields in the IPv4 address.
4. End Anchor ($): Ensure that the string ends at the end means that all numeric fields have matched.

Example usage:

The following code example demonstrates how to match IPv4 addresses using regular expressions in Python:

 <code class="python">import re ip_address = "192.168.1.1" if re.match(r"^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$", ip_address): print("有效的IPv4 地址") else: print("无效的IPv4 地址")</code>

Output:

<code>有效的IPv4 地址</code>

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