Automatically relaunch a closed macOS application

Here is my launchd script to keep SomeApp always running.

Name it SomeApp.restart.plist and place it in ~/Library/LaunchAgents/

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>RunAtLoad</key>  
        <true/>  
        <key>KeepAlive</key>
        <true/>
        <key>Label</key>
        <string>SomeApp.restart</string>
        <key>ProgramArguments</key>
        <array>
                <string>/path/to/SomeApp.app/Contents/MacOS/SomeApp</string>
        </array>
</dict>
</plist>

Load it once with

launchctl load ~/Library/LaunchAgents/SomeApp.restart.plist

Launchctl will run this after reboots.

• RunAtLoad will launch the application the first time launchctl runs this
• KeepAlive will restart it if the application quits (CMD+Q or crash)

Should run forever. If you want a GUI tool to help, Lingon works even though development has stopped.

You could write a launchd script to do it. Launchd can watch for applications and restart them if they disappear. I might have one somewhere if you are interested.

Updated with an example...

See mankoff's example. Here's mine, it's slightly different but works the same...

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">  
  <dict>  
    <key>RunAtLoad</key>  
    <true/>  
    <key>KeepAlive</key>  
    <true/>  
    <key>Label</key>  
    <string>keep.it.running</string>  
    <key>Program</key>  
    <string>/Applications/Address Book.app/Contents/MacOS/Address Book</string>  
</dict>  
</plist>