It needs to be in your computer's /bin/, not your phone's. Actually, it can be anywhere as long as it's on your $PATH. It's usually suggested that you create a /bin/ directory at your home folder (~) and then run all your personal binaries from there, then you can include that /bin/ in your .bashrc so that it gets loaded on every new terminal.
Open up a terminal window and do either
or
depending on which editor you're comfortable with. Add the following to the end of your .bashrc
Code:
PATH=$PATH:/path-to-home/bin/
export PATH
where path-to-home is, ofcourse, the path to your home folder (usually /home/username), you can't use the ~ wildcard in the .bashrc script.
After you have your ~/bin set up, restart the terminal then move the unyaffs binary to ~/bin/ and then chmod a+x it, that way you can run the tool from any location.
To run the tool, just pass an image file as a parameter, note that the contents will be output to the directory where the image file is stored, so say I have a hero system file on my Desktop:
Code:
~$ cd ~/Desktop
~/Desktop$ mkdir HeroSystem
~/Desktop$ mv system.img HeroSystem
~/Desktop$ cd HeroSystem
~/Desktop/HeroSystem$ unyaffs system.img
end of file.
~/Desktop/Herosystem$_
The contents, along with the system.img will be in ~/Desktop/HeroSystem
) and compiled it myself. 
