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Network Patterns

Match IPv4 Address Regex

A regular expression to validate and extract standard IPv4 IP addresses from logs or text.

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How to Match an IPv4 Address with Regex

Validating an IPv4 address is one of the most common tasks in network programming and log parsing. A standard IPv4 address consists of four octets, ranging from 0 to 255, separated by dots.

The Pattern Breakdown

The regular expression ^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$ looks complex, but it simply enforces the mathematical rules of an IP address:

  • 25[0-5]: Matches numbers 250 through 255.
  • 2[0-4][0-9]: Matches numbers 200 through 249.
  • [01]?[0-9][0-9]?: Matches numbers 0 through 199.

Common Use Cases

  • Log Parsing: Extracting client IPs from Nginx or Apache access logs.
  • Firewall Rules: Validating user input in security configurations.
  • Data Cleaning: Sanitizing CSV files containing server metadata.