正则表达式匹配范围0-255，没有^和$

Question

有没有办法在没有^和$的情况下匹配一系列数字（0-255）？

匹配数字

• 1
• 12
• 123

不匹配的数字

• 1234
• 555

Answer 1

您可以使用lookahead和lookbehind来匹配仅 1-3位数。

(?<!\d)(?:[1-9]?\d|1\d\d|2(?:[0-4]\d|5[0-5]))(?!\d)

Regex101 demo

Answer 2

Not using anchor characters, BrightOne was wise to integrate lookarounds for numeric characters. However, the pattern isn't fully refined. To optimize the pattern for speed and maintain accuracy:

1. Use quantifiers on consecutive duplicate characters.
2. Organize the alternatives not in sequential order but with quickest mis-matches first.
3. Avoid non-essential capture (or non-capture) groups. (despite seeming logical to condense the "two hundreds" portion of the pattern)

This is my suggested pattern: (Demo)

/(?<!\d)(?:1\d{2}|2[0-4]\d|[1-9]?\d|25[0-5])(?!\d)/  #3526 steps

(Brightone's pattern resolves in 5155 steps)
(treesongs' second pattern resolves in 5184 steps) *at time of posting, the first pattern was inaccurate)