To check what shell you are using right now, type:
grep $USER /etc/passwd
To change your shell, type
chsh
chsh shows first the current shell and then prompts for the new shell. Less experienced users may choose tcsh instead. The shell will be changed permanently in few hours after typing the tcsh. For a temporary shell change type the name of the shell on the command prompt.
For example, type
sh
to work in bourne shell immediately. The sh prompt,$,
appears and you can enter sh commands, say,
ls
cd cs241
mkdir lab2
pwd
Once finished, you may end the work and return to the previous shell using CTRL-D.
Notice that most UNIX commands introduced till now are valid in all shells. From now on, when discussing interactive use, we focus on c-shell or tc-shell only. The valid syntax for korn shell or bourne shell can be found in UNIX in a nutshell book.
Before discussing internal and external commands, we need to understand the structure of the filesystem in UNIX.