Question

Is there a way in bash on a mac to draw a pretty info box that displays a simple message like “please save all files to /Users/……”

Answer 1

You can run fragments of applescript from you bash scripts.
A simple popup would look like this:

#!/bin/bash
/usr/bin/osascript <<-EOF

    tell application "System Events"
        activate
        display dialog "Hello world"
    end tell

EOF

This will feed the applescript between the EOF tags to osascript and execute it
(resulting in a Hello World popup).