I downloaded google-chrome for Linux, it got downloaded as a .deb file in downloads folder. I changed the current directory to the downloads folder and ran "google-chrome" in terminal. It started google chrome, but the issue is that .deb file is not a script(as I understand). Then how did the terminal understand that the 'google-chrome' command meant to start it? Commands like emacs...etc are already built-in. What about this command which is new to bash? How did it recognise it?
First a few basics:
When you run a command on your terminal, you enter the name of a file, (which should be executable): if you enter a simple name e.g.
emacs, the system searches a number of directories for a file with such name. This list of directory is your
PATH (i.e. it is stored in a variable named PATH). you can see its contents by typing
echo $PATH. (As a side note, these commands are not built-in like you said in your question... but some are, for instance
ls, which don't have any executable file, but is directly executed by the shell)
Alternatively, you can enter a more complex filename, which include the directory :
/usr/bin/emacs, or event relative pathnames ! For instance, if you want to run the program in the file
myprog, residing in your user directory, enter
. meaning current directory)
Now back to your question:
When installing software, the system has to take care of putting everthing in the right place, so you can find it later on... It is what the package manager does : it takes an archive (.deb file), open it, and basically, put the files in the right places.
In conclusion, you have to open your .deb file with the package manager.
cd ~/Downloads dpkg -i google-chrome.deb
or, event better, install it through the software center.
You probably already had google-chrome installed on your computer.
A deb file contains all the necessary files to install it with dpgk (as root):
dpkg -i <your-google-chrome-deb-file>.deb
dpkg will copy binaries to you binary files location and then the command google-chrome will be available in your shell. If you didn't do this nor used an apt-get to install google chrome, I guess it means that google chrome was already present on your system.
If you want to see what the deb fils contains, you can use:
dpkg --contents <file>.deb
There are chromium and chrome if I'm not mistaken! It could be any one of those you already install.