How can you active the Script Menu Bar with AppleScript?
10.13 (High Sierra) and before

If you do not want to have to go through Script Editor > Preferences > General to check the [ ] Show Script menu in menu bar check box, then here is one way of enabling the Script Menu using AppleScript:

tell application "System Events"
    if not (script menu enabled) then
        tell current application
            do shell script "open '/System/Library/CoreServices/Menu Extras/Script Menu.menu'"
        end tell
    end if
end tell


You could just use:

do shell script "open '/System/Library/CoreServices/Menu Extras/Script Menu.menu'"


However, since System Events has a script menu enabled property, it makes sense to check whether or not it's enabled first. Either way though, opening the target file loads the Script Menu and checks the [√] Show Script menu in menu bar check box in: Script Editor > Preferences > General

Also, from Terminal, you could just run:

open '/System/Library/CoreServices/Menu Extras/Script Menu.menu'


Opening the target file in any manner shown accomplishes the goal.

By the way, when the Script Menu is enabled the target plist file is:

com.apple.systemuiserver.plist


The key is a Boolean and is NSStatusItem Visible com.apple.scriptmenu, and will also have an element in the menuExtras Array as a String holding the pathname of the item.

Note that the information above was gathered under macOS 10.13.5.



10.14 (Mojave) and up

The script menu has been upgraded into a full-fledged application, instead of a .menu file. It is now located at /System/Library/CoreServices/Script Menu.app.

To activate it on 10.14+, the terminal/shell command changes to:

open '/System/Library/CoreServices/Script Menu.app'