Invoking GNOME Activities overview from command line

A command that causes the shell to switch to the overview is:

dbus-send --session --type=method_call --dest=org.gnome.Shell /org/gnome/Shell org.gnome.Shell.Eval string:'Main.overview.show();'

Use Main.overview.hide(); to close the overview, or Main.overview.toggle(); to toggle between overview and normal view (with thanks to gatr and Marcelo Avila).

There might be a proper command line way to interact with various GNOME Shell components (using DBus, I suppose), but a quick and dirty way is to simulate the keypress:

xdotool key super