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Introduction to the Command Line Interface

Overview

An operating system Kernel’s job is to provide services so that softwares can communicate with hardware. It manages computer system hardware, memory, and processes (among all others). Its services are exposed via the system call interface, which in itself is wrapped in C standard Library to provide an API that user applications can interact with. Various user applications are made so that the OS services are usable to humans. These services are those you encounter daily when using a computer, for example:

  • File management (rename, create, list files, delete, etc),
  • Process management (run and terminate),
  • System diagnostics (RAM used, CPU %, disk space),
  • I/O operations like printing, reading from disk, communication via network, resource management (overclock speed, VM size),
  • Protection (security and permission settings), etc.

The Shell

A shell is one of these user applications that acts as an interface to allow users to access OS services. It is named shell because it is seen as an “outer” layer around the OS kernel. OS shells are made either in a form of command-line interface (CLI, also known as terminal) where users can provide commands via text, or graphical user interface (GUI) where users can provide commands via mouse clicks. In this lab, we are going to learn a little bit about the command-line interface, bash scripting, and makefiles.

You would need to install any POSIX-compliant OS before coming to this lab. The guide is provided in our course handout.

In order for us to be able to use CLI, we need to be familiar with their commands and their calling syntax. In particular, we are concerned with UNIX-type shells (POSIX is an IEEE standard that acts as a standard UNIX version) in this course.

  • Open your terminal/command line window.
  • The terminal window in front of you contains a shell, which enables you to use commands to access OS services.

Submission

The total marks for this lab is 20. Please answer the questionnaire provided on eDimension Week 1. You are to score any 20 points for this lab.

Task 1

TASK 1: To find your current shell, type the command: ps -p $$

bash-3.2$ ps -p  $$
  PID TTY           TIME CMD
70846 ttys003    0:00.01 bash
bash-3.2$

Bash shell (bash is used in the screenshot above. There are other shells as well: z-shell) or fish. Which one to choose? It is entirely up to you.

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