Launching Scripts #4: AppleScript from Shell Script

In the last post, we discussed how to run shell commands and scripts from an Apple Script environment. In this post, we will look at how we can run AppleScript commands and scripts from the shell environment.

Open Scripting Architecture

The key to running AppleScript from the shell is the osascript command. OSA is short for ‘Open Scripting Architecture’ which is the framework that powers AppleScript. This framework allows AppleScript to have its native language, but also use JavaScript syntax.

The osascript command allows us to run AppleScript commands from Terminal and shell. The most common use is the user interaction commands from AppleScript, like display dialog:

osascript -e 'display dialog "Hello from shell"'

The -e option tells osascript that it will get one or more lines of statements as arguments. The following argument is AppleScript code. You can have multiple -e options which will work like multiple lines of a single AppleScript:

> osascript -e 'display dialog "Hello from shell"' -e 'button returned of result'
OK

osascript prints the value of the last command to stdout. In this case, it is the label of the button clicked in the dialog. (The ‘Cancel’ button actually causes the AppleScript to abort with an error, so no label will be returned for that.)

When you have multiple lines of script, using multiple -e statements will quickly become cumbersome and unreadable. It is easier to use a heredoc instead:

osascript <<EndOfScript
   display dialog "Hello from shell"
   return button returned of result
EndOfScript

This also avoids the problem of nested quotation marks and simplifies shell variable substitution.

Shell variables and osascript

There are a few ways to pass data into osascript from the shell.

Since the shell substitutes variables with their value before the command itself is actually executed, this works in a very straightforward manner:

computerName=$(scutil --get ComputerName)

newName=$(osascript -e "text returned of (display dialog \"Enter Computer Name\" default answer \"$computerName\")")

echo "New Name: $newName"

This works well, but because we want to use shell variable substitution for the $computerName, we have to use double quotes for the statement. That means we have to escape the internal AppleScript double quotes and everything starts to look really messy. Using a heredoc, cleans the syntax up:

computerName=$(scutil --get ComputerName)

newName=$(osascript <<EndOfScript
    display dialog "Enter Computer Name" default answer "$computerName"
    return text returned of result
EndOfScript
)

echo "New name: $newName"

I have a detailed post: Advanced Quoting in Shell Scripts.

Environment Variables

Generally, variable substitution works well, but there are some special characters where it might choke. A user can put double quotes in the computer name. In that case, the above code will choke on the substituted string, since AppleScript believes the double quotes in the name end the string.

If you have to expect to deal with text like this, you can pass data into osascript using environment variables, and using the AppleScript system attribute to retrieve it:

computerName=$(scutil --get ComputerName)

newName=$(COMPUTERNAME="$computerName" osascript <<EndOfScript
    set computerName to system attribute "COMPUTERNAME"
    display dialog "Enter Computer Name" default answer computerName
    return text returned of result
EndOfScript
)

echo "New name: $newName"

The shell syntax

VAR="value" command arg1 arg2...

sets the environment variable VAR for the process command and that command only. It is very useful.

Retrieving environment variables in AppleScript using system attribute is generally a good tool to know.

Interpret this!

osascript can also work as a shebang. That means you can write entire scripts in AppleScript and receive arguments from the shell. For example, this script prints the path to the front most Finder window:

#!/usr/bin/osascript

tell application "Finder"
    if (count of windows) is 0 then
        set dir to (desktop as alias)
    else
        set dir to ((target of Finder window 1) as alias)
    end if
    return POSIX path of dir
end tell

You can save this as a text file and set the executable bit. I usually use the .applescript extension.

> print_finder_path.applescript
/Users/armin/Documents

To access arguments passed into a script this way, you need to wrap the main code into a run handler:

#!/usr/bin/osascript

on run arguments
    if (count of arguments) is 0 then
        error 2
    end if
    return "Hello, " & (item 1 of arguments)
end

You can combine this into a longer script:

macOS Privacy and osascript

When you ran the above script, you may have gotten this dialog:

If you didn’t get this dialog, you must have gotten it at an earlier time and already approved the access.

AppleEvents between applications are controlled by the macOS Privacy architecture. Without this, any process could use AppleEvents to gather all kinds of data from any process. These dialogs are easy enough to deal with when running from Terminal. But if you put your AppleScript code (or shell scripts calling AppleScript) into other apps or solutions, it could get messy quite quickly.

Mac Admins generally want their automations to run without any user interactions. You can avoid these dialogs by creating PPPC (Privacy Preferences Policy Control) profiles that are distributed from an MDM server. In this case you have to pre-approve the application that launches the script, which can sometimes also be challenge. The other option is to find solutions that avoid sending AppleEvents altogether.

I have a longer post detailing this: Avoiding AppleScript Security and Privacy Requests

osascript and root

Management scripts often run as a privileged user or root. In this case, certain features of AppleScript may behave strangely, or not at all. I generally recommend to run osascript in the user context, as detailed in this post: Running a Command as another User

Conclusion

AppleScript’s bad reputation may be deserved, because its syntax is strange, and often very inconsistent. Nevertheless, it has features which are hard to match with other scripting languages. You can use the strategies from this and the previous posts to combine AppleScript with Shell Scripting and other languages to get the best of both worlds.