More specifically, to grab the list of a user's login items, something like this should work:
CurUser=$(ls -l /dev/console | awk '{print $3}')
defaults read /Users/$CurUser/Library/Preferences/com.apple.loginitems.plist | grep Name
On the other hand, AppleScript run in Terminal looks like it can manipulate/read these values better than defaults (because the values are deeply nested within the plist):
# delete login item
osascript -e 'tell application "System Events" to delete login item "itemname"'
# list loginitems
osascript -e 'tell application "System Events" to get the name of every login item'
I pulled those commands from this gist, so give that a once over and see if it works for your needs.
