gsettings set org.gnome.metacity theme “Arc-Dark” # For good measure… gsettings set org.gnome.desktop.interface gtk-theme ‘Arc-Dark’ gsettings set org.gnome.desktop.wm.preferences theme ‘Arc-Dark’ Window Decorations on Gnome Flashback not changing

template.txt contains: Hello ${NAME} Then you could run: export NAME=Dan envsubst < template.txt And the result would be "Hello Dan"