The shell commands are the basic utilities provided by the UNIX shell, which can be viewed as a command interpreter. The default and most commonly used shell is bash (/bin/bash). (Others possible are listed in the file /etc/shells.) These shells not only provide the user environment but are also powerful programming languages. The login command initializes the user, and group IDs and the working directory, then executes a command interpreter, the login shell, according to the specifications found in a password file. The default can be altered in your password file but only by a super-user with the required authority or protection code.
The .bash_profile and .bashrc files contain various shell commands for setting up various environment parameters and default values. The commands in these files, once set up, are executed every time you login, as in the case of .bash_profile, or every time you invoke the shell, as in the case of .bashrc.
A fairly complete list of available shell commands and features follows. These include most of the widely used and much needed commands. You can of course refer to the online manual for further assistance. As stated before, these commands are mostly used in the special setup files. Examples of such files are given in the section on Setting Up Your Own Environment.