:13079:1014:Charles Stross:/u/charles:/bin/ksh
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Because the different shells understand different commands, it is important to know which shell you are working in. To find out what your login shell is, type grep $LOGNAME /etc/passwd (LOGNAME is the environment variable that stores your login name). You will see something like the following line:
charles:The last field of this line (after the last colon (:)) is the login shell executed for the user named in the first field on the line.
(This line is a record from the /etc/passwd file, a database that identifies the home directory, login name, group ID, permissions, and login shell for every user on the system. Only the system administrator can change this file.)
You can run a shell interactively as a subprocess (often called a subshell) by typing its name (for example, csh). Your subsequent commands are interpreted by the subshell until you type the command exit to quit the shell. The system is set up to load one particular shell for you every time you log in.
If you want to change your login shell, for example to switch to the Korn shell on a permanent basis, ask your system administrator.