regex search to find files not containing a string

You can run a regular expression search which will find any files which do not contain a word or phrase that you designate.

In this example we have a set of text files, only one of which contains the word, 'panda'.

Using a text editor like NotePad ++ we run the following search to locate any files which do not have this string:

(?s)\A((?!panda).)+\z

. . . use the option to Find All using the Find in Files tool, and only the files in the folder in which you search which do not contain the string will be listed in the results pane.