Changing Shells

Determining Your Login Shell

Your system may already be configured with the shell you want to use. You can display the file name of the shell you entered when you logged in by typing:

The echo command displays the contents or value of a variable named SHELL. The SHELL variable contains the name of the file that contains the shell program that you are running. The system responds to your echo $SHELL command with something like the following:

/bin/posix/sh
$ _

In this case, it is /bin/posix/sh, the file that contains the code for the POSIX Shell. Table 1-2 “Shell File Names and Default Prompts” lists both the file name that displays for each shell and the default system prompt.

Temporarily Changing Your Shell

Unless you are in a restricted shell, you can temporarily change your shell by using this command:

where shell_name is the name of the shell (for example, /bin/sh, or /bin/ksh). Temporarily changing your shell lets you experiment in other shells. By typing the name of the shell you want to run, you invoke (enter) that shell, and the correct prompt is displayed. After experimenting in the new shell, return to your original shell by typing either exit or pressing CTRL-D.

The following example begins in the Bourne Shell, enters the Korn Shell, and returns to the Bourne Shell:

$ /bin/ksh                    Enter Korn Shell.
$ ps                          Execute the ps command.
   PID TTY      TIME COMMAND  
  6009 tty01    0:00 ksh      Notice
that both the Korn Shell and
  5784 tty01    0:00 sh       Bourne Shell processes are running.
  6010 tty01    0:00 ps       
$ exit                        Exit Korn Shell.
$ _                            Bourne Shell returns.

Permanently Changing Your Shell

To permanently change your login shell (the default shell you get when you log in), use the chsh (change shell) command:

where username is your user name and shell_path_name is the full path name (e.g., /bin/posix/sh) of the shell you want as your default. Table 1-2 “Shell File Names and Default Prompts” contains the full path name for each of the shells. After you use the chsh command, you must log out and log in again for the change to take effect. For example, if terry changes the default login shell to the Korn Shell, the command reads:

$ chsh terry /bin/ksh
$ _