Add app to OSX “Login Items” during a Package Maker installer postflight script

Here’s the options I investigated and experimented with:

Option 1: Use Login Items

This is the method I used. It’s very easy to do from a bash file by adding the following line to your postflight.

defaults write /Library/Preferences/loginwindow AutoLaunchedApplicationDictionary -array-add '{Path="/Applications/Your Application.app";}'

Note: You don’t even have to worry about adding duplicates if you reinstall the application. The loginwindow process removes duplicates when it reads them.

I tested this on 10.5, 10.6, and 10.7
@noa says this doesn’t work on mountain lion (10.8), Haven’t personally confirmed.

Option 2: LaunchAgent

The unique ramifications of using a Launch Agent are:

1. Your application doesn’t appear in the Login Items list, so the
   user really has to know what they’re doing to get rid of it
2. The user cannot end your applications process without running:
   launchctl unload /Library/LaunchAgents/com.your.package.plist

Here’s some code you could use to create the launch agent in your bash file:

cat > /Library/LaunchAgents/com.your.application.agent.plist << EOT
<?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>Label</key>
    <string>com.your.application.agent</string>
    <key>ProgramArguments</key>
    <array>
        <string>/Applications/Your Application.app/Contents/MacOS/Your Application</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
</dict>
</plist>
EOT

Option 3: Compile Obj-c code to a binary

I never actually finished this approach. Apparently, this is the approach that Novell takes. Essentially you’d make a foundation application that calls the libraries referenced from this solution:
How do you make your App open at login?

Other

Didn’t try this but according to this post if you want it to work on tiger you need to use AppleScript..? I can’t confirm or deny that but thought this link might be relevant.
Editing Mac OS X login items in Objective-C through AppleScript