But really, it's 2015. Are you really using a terminal emulator without a buffer search? Are you not using screen or tmux, both of which can do these things natively, with no external tools? Why? And what is wrong with backgrounding the tail command, running your grep, and then foregrounding the tail command?
Personally? The reason I'm not using screen is that there's no way to atomically [attach, create new window] in screen and I value my gnome-terminal tabs.
If tmux can do that, then I'd consider it reason to switch.
Check out 'byobu'. Stupid name, but it's built on screen and can use the screen commands. Byobu has F2 for new terminal tab, F3/4 to shuffle between them.
Depending on what you mean by "atomic" (do you really mean atomic, or do you just not want to have to type anything after you've attached to create the new window?), you can do this with screen's -X option. If that's what you want to do I can try to dig up the way I used to do this.
Do you mean creating a new window every time you attach to an existing session? Or do you mean that each of those actions ("attach" and "create new window") should be atomic?
But really, it's 2015. Are you really using a terminal emulator without a buffer search? Are you not using screen or tmux, both of which can do these things natively, with no external tools? Why? And what is wrong with backgrounding the tail command, running your grep, and then foregrounding the tail command?