In Linux terminal, how to delete all files in a directory except one or two

Question

In a Linux terminal, how to delete all files from a folder except one or two?

For example.

I have 100 image files in a directory and one

Answer 1

In bash, you can use:

$ shopt -s extglob  # Enable extended pattern matching features    
$ rm !(*.txt)       # Delete all files except .txt files