Comment 2 for bug 505140

Colin, I'll rather propose that (simplifying the code):

     # Prevent from updating if parameters already present (persistent usb key)
     if ! `grep -qs 'AutomaticLoginEnable' $GDMCustomFile` ; then
        if ! `grep -qs '\[daemon\]' $GDMCustomFile` ; then
            printf '[daemon]' >> $GDMCustomFile
        fi
        sed -i "s/\[daemon\]/\[daemon\]\n$AutologinParameters/" $GDMCustomFile
     fi

With that, we handle every cases:
- no GDMCustomFile, create the autologin part with [daemon]
- GDMCustomFile already exists with [daemon] section but without the autologin part (case of ubutu derivatives): add it
- GDMCustomFile exists without [daemon] section: add all the autologin stuff and the section (don't know if that can happen with current GDM implementation, but it'll surely later)
- GDMCustomFile exists with [daemon] section and autologin stuff in place (case of persistent usb key): don't do anything

And we get our \n interpreted by sed :)
This new proposal is in my linked branch.