The Wiert Corner – irregular stream of stuff

Interesting piece: Don’t Use Regular Expressions To Parse IP Addresses! [WayBack]

TL;DR:

• for IPv4, use inet_aton [WayBack] when available
• for IPv6, use getaddrinfo [WayBack] when available
• networking – Are IP addresses with and without leading zeroes the same? – Super User It depends! [WayBack]

When have neither then for quad-dotted decimal IPv4 addresses (ignoring for instance octals and grouped quads), this is suitable: regex – Regular expression to match DNS hostname or IP Address? – Stack Overflow [WayBack]

ValidIpAddressRegex = "^(([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])$";

Which explained looks like this:

https://regex101.com/r/Wyr2Zd/1

Regular expression:

/ ^(([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])$ / g

Explanation:

• ^ asserts position at start of the string
  • 1st Capturing Group (([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}
    • {3} Quantifier — Matches exactly 3 times
      A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you’re not interested in the data
      • 2nd Capturing Group ([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])
        • 1st Alternative [0-9]
          • Match a single character present in the list below [0-9]
0-9 a single character in the range between 0 (ASCII 48) and 9 (ASCII 57) (case sensitive)
        • 2nd Alternative [1-9][0-9]
          • Match a single character present in the list below [1-9]
1-9 a single character in the range between 1 (ASCII 49) and 9 (ASCII 57) (case sensitive)
          • Match a single character present in the list below [0-9]
0-9 a single character in the range between 0 (ASCII 48) and 9 (ASCII 57) (case sensitive)
        • 3rd Alternative 1[0-9]{2}
          • 1 matches the character 1 literally (case sensitive)
          • Match a single character present in the list below [0-9]{2}
{2} Quantifier — Matches exactly 2 times
            0-9 a single character in the range between 0 (ASCII 48) and 9 (ASCII 57) (case sensitive)
        • 4th Alternative 2[0-4][0-9]
          • 2 matches the character 2 literally (case sensitive)
          • Match a single character present in the list below [0-4]
0-4 a single character in the range between 0 (ASCII 48) and 4 (ASCII 52) (case sensitive)
          • Match a single character present in the list below [0-9]
0-9 a single character in the range between 0 (ASCII 48) and 9 (ASCII 57) (case sensitive)
        • 5th Alternative 25[0-5]
          • 25 matches the characters 25 literally (case sensitive)
          • Match a single character present in the list below [0-5]
0-5 a single character in the range between 0 (ASCII 48) and 5 (ASCII 53) (case sensitive)
      • \. matches the character . literally (case sensitive)
  • 3rd Capturing Group ([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])
    • 1st Alternative [0-9]
      • Match a single character present in the list below [0-9]
        0-9 a single character in the range between 0 (ASCII 48) and 9 (ASCII 57) (case sensitive)
    • 2nd Alternative [1-9][0-9]
      • Match a single character present in the list below [1-9]
1-9 a single character in the range between 1 (ASCII 49) and 9 (ASCII 57) (case sensitive)
      • Match a single character present in the list below [0-9]
0-9 a single character in the range between 0 (ASCII 48) and 9 (ASCII 57) (case sensitive)
    • 3rd Alternative 1[0-9]{2}
      • 1 matches the character 1 literally (case sensitive)
      • Match a single character present in the list below [0-9]{2}
{2} Quantifier — Matches exactly 2 times
        0-9 a single character in the range between 0 (ASCII 48) and 9 (ASCII 57) (case sensitive)
    • 4th Alternative 2[0-4][0-9]
      • 2 matches the character 2 literally (case sensitive)
      • Match a single character present in the list below [0-4]
0-4 a single character in the range between 0 (ASCII 48) and 4 (ASCII 52) (case sensitive)
      • Match a single character present in the list below [0-9]
0-9 a single character in the range between 0 (ASCII 48) and 9 (ASCII 57) (case sensitive)
    • 5th Alternative 25[0-5]
      • 25 matches the characters 25 literally (case sensitive)
      • Match a single character present in the list below [0-5]
0-5 a single character in the range between 0 (ASCII 48) and 5 (ASCII 53) (case sensitive)
• $ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
• Global pattern flags
  g modifier: global. All matches (don’t return after first match)

–jeroen