Terms

Utilities

Utilities are programs, such as who and date, that you can run or execute.

Commands

A command is the name of a program and any arguments you specify to that program to cause its behavior to change. You might see the term command used instead of the term utility for simple commands, where only the program name to execute is given.

Kernel

The kernel is the heart of the UNIX system. It provides utilities with a means of accessing a machine’s hardware. It also handles the scheduling and execution of commands.

Uninitialized Shell

When a shell is started it is uninitialized. This means that important parameters required by the shell to function correctly are not defined.

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.

Interactive Mode

In interactive mode the shell reads input from you and executes the commands that you specify. This mode is called interactive because the shell is interacting with a user.

Noninteractive Mode

In noninteractive mode, the shell does not interact with you; instead it reads commands stored in a file and executes them. When it reaches the end of the file, the shell exits.

Shell Script

A shell script is a list of commands stored in a file that the shell executes noninteractively.

Home Directory

Your home directory is the directory in which you start out after you log in.

Comments

A comment is a statement that is embedded in a shell script but should not be executed by the shell.

Man Pages

Every version of UNIX comes with an extensive collection of online help pages called man pages (short for manual pages). The man pages are the authoritative source about your UNIX system. They contain complete information about both the kernel and all the utilities.