JAVASCRIPT

regex do not contain

^((?!word).)*$

// Test
/^((?!word).)*$/gi.test('Should not contain word') // Returns false
/^((?!word).)*$/gi.test('John Doe') // Returns true

regex not contain

^((?!hede).)*$

regex not contains

^(?!keyword).*
 // Regex pattern to find lines that do not contain keyword, incl newline