If you need to use the adb tool that comes with the Android SDK, you can easily add it to the command line.

This example is on OS X, but also works on different Linux distros such as Ubuntu.

The adb executable is located in the /platform-tools folders, where is the path to here you installed (unzipped) the Android SDK.

Open a terminal, and type echo $PATH. This is your systems PATH variable, containing a list of folders separated by a colon.  We will be adding the folder path to this PATH variable.

We can add a folder to the PATH variable by running the following command:

export PATH=/Users/<username>/dev/sdk/platform-tools:$PATH

This will add my tools folder to the PATH variable, so I can easily use the adb program from that folder.
Verify that it was added by typing the echo $PATH command again.

Close the terminal, open a new one, and run adb version.
It should output:

Android Debug Bridge version 1.0.31