Shells on a Linux system:

The file /etc/shells gives an overview of known shells on a Linux system:

$ cat /etc/shells 

    /bin/bash 

    /bin/sh 

    /bin/tcsh 

    /bin/csh

Your default shell is set in the /etc/passwd file, like this line for user euclid:

euclid:L2NOfqdlPrHwE:504:504:Euclid:/home/euclid:/bin/bash

To switch from one shell to another, just enter the name of the new shell in the active terminal. The system finds the directory where the name occurs using the PATH settings, and since a shell is an executable file, the current shell activates it and it gets executed. A new prompt is usually shown, because each shell has its typical appearence:

$ tcsh 

    [euclid@machine ~]$