Apple - How can I make an Automator service run a shell script and display the output?

Nice and clean solution is to display message via Notification Center. Just execute the following terminal command in your script.

osascript -e 'display notification "All files converted" with title "ffmpeg converter"'

'osascript' command runs any AppleScript from terminal, 'display notification' pops up nice notification.

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Also you can use 'display alert'. It has no limitation of message length and it's easy to add OK button to it.

osascript -e 'set alertResult to display alert "Bad news :( Error converting your video file." buttons {"OK"} as warning'

Here is Apple Script commands reference. Look for 'display notification' and 'display alert' for more information.

This AppleScript will launch a Terminal window with the command you specified:

on run {input, parameters}
    tell application "Terminal"
        activate
        set filesString to ""
        repeat with file_ in input
            set filesString to filesString & " " & quoted form of (POSIX path of file_)
        end repeat
        do script "for f in" & filesString & "; do
/usr/local/bin/ffmpeg -i \"$f\" -c:v libx264 -vf yadif -pix_fmt yuv420p -crf 21 -preset slow -movflags faststart -c:a copy ${f%.*}_h264_yadif.mov
done"
    end tell
    return input
end run

Create a “Run AppleScript” action in Automator and paste it in there.

Here's a simple solution that I got working, which shows the command output once it's finished:

1. Pass the output of a Run Shell Script action to Set Value of Variable
2. Use that variable to, for example, display a notification.

For example, with the test.py Python script, all I'm doing is printing the arguments passed (“Running a script with …”), so when I run it, after finishing, it shows: