Regex "(?<!\d)"

[boris]

What does the regex in my question's title above mean?

Source: Search Language Quick Reference Card (on top of page 3)

Context: "(?<!\d)" is part of this full example:

| regex _raw="(?<!\d)10.\ d{1,3}\.\d{1,3}\.\d{1,3} (?!\d)"

for finding this type of string:

10.0.0.0/8

I understand this part:

10.\ d{1,3}\.\d{1,3}\.\d{1,3}

10.0.0.0

I am also uncertain about this end part:

(?!\d)

[boris · Accepted solution]

(?<!a)b

matches a "b" that is not preceded by an "a"

Example:

(?<!\d)f 

would find the letter f as long as it wasn't like 5f.

(?<=a)b 

is the opposite. A positive look behind.