Remove all files except some

rm_exclusion.sh

#!/bin/bash

# Enable Extended Globbing
shopt -s extglob

# Simple version
rm !(a|b|c)

# Scriptable version
function join_by {
        local IFS="$1"
        shift
        echo "$*"
}

KEEP=( "a" "b" "c" )
rm !($(join_by "|" "${KEEP[@]}"))