need the script for back button emulation

can someone tell me what script/command I need to run on a rooted phone to emulate android's hardware back button?

I'm trying to create a always-on-screen back button and its code is all set. Now I'm looking for a script/command which can emulate android's hardware back key press and set it to whatever app is active. something like http://forum.xda-developers.com/showthread.php?p=9575198 and http://forum.xda-developers.com/showthread.php?t=865525

What i'm looking would be a shell command like "su event_command back_ke开发者_如何学Pythony_code"

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Just call:

finish();

It will kill the current activity and remove it from the stack returning the user to the previous activity. Much like the back button does.

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Process process = Runtime.getRuntime().exec("sendevent /dev/input/event3 1 158 1")

158 is the value of the back button in android

something like this should work although not tested of course you need to ask for root first