rm
The command used to remove files.
scalar variable
A scalar variable can hold only one value at a time.

sed
The sed command is a stream editor that allows you to modify input lines using regular expressions.

set group ID (SGID)
The SGID permission causes a script to run with its group set to the group of the script, rather than the group of the user who started it.

set user ID (SUID)
The SUID permission causes a script to run as the user who is the owner of the script, rather than the user who started it.

shell
Provides you with an interface to the UNIX system. It gathers input from you and executes programs based on that input. After a program has finished executing, the shell displays that program’s output. The shell is sometimes called a command interpreter. See also bash, Bourne shell, C shell, Korn shell, and tcsh.

shell initialization
After a shell is started it undergoes a phase called initialization to set up some important parameters. This is usually a two step process that involves the shell reading the files /etc/profile and .profile.