add built-in help

entrypoint.sh

@@ -4,6 +4,28 @@
 ### run supplied CMD
 #
 
-exec "$@"
+convertCase () {
+    printf "%s" "$1" | tr "[:upper:]" "[:lower:]"
+}
+
+# check if requesting help
+isHELP=$( convertCase "$1" )
+if [ "$isHELP" = 'help' ]; then
+    # display help
+    printf "\n\n--- ab-netcat usage ---\n\n"
+    printf "This container can be run in several ways, more details in the repo wiki at https://git.asifbacchus.app/ab-docker/ab-netcat/wiki\n\n"
+    printf "In all cases, this container is a persistent listener. General execution is:\n"
+    printf "docker run [-d|-it] --init --rm -p [<ipaddr>:]<host port>:5555 [--name ab-netcat] [-e TZ=timezone] docker.asifbacchus.app/ab-netcat\n\n"
+    printf "neither '-d' or '-it': Run in the foreground and display what's being received.\n\n"
+    printf "'-d': Run detached, you will have to run 'docker logs -f ab-netcat' to see what the container is receiving from connected client(s).\n\n"
+    printf "'-it': Run interactively. You can respond to clients or even chat :-)\n\n"
+    printf "'--init': This allows you to use ctrl-c to terminate container instead of having to run 'docker stop ab-netcat' or 'docker rm -f ab-netcat'. Only useful when running in the foreground or interactively.\n\n"
+    printf "'-e TZ=timezone': The container will default to UTC time, but you can change it using this environment variable. Ex: '-e TZ=America/Edmonton'\n\n"
+    printf "You can run the container and supply '/bin/sh' after the container name if you want to be dumped to a shell instead of automatically running netcat. If you're doing that, remember to also pass '-it':\n"
+    printf "Ex: docker run -it --rm -p 127.0.0.1:5555:5555 docker.asifbacchus.app/ab-netcat /bin/sh\n"
+    printf "\n--- end of help ---\n\n"
+else
+    exec "$@"
+fi
 
 #EOF