Lab No. 1

After completing this lab, students will be able to:

  • Describe what a shell is.
  • Login and end a shell session (ssh, logout and exit)
  • Execute and edit commands on a shell.
  • Distinguish between commands, command options and arguments when providing input to the shell

The Shell

A shell is interactive command interpreter: a program that takes text input from the user in the form of commands and arguments, instructs the operating system to execute the tasks specified by the user input, and provides output that results from the execution of the commands by the operating system.

Access to a shell is typically obtained though software known as a terminal emulator, which in this day an age is simply referred to as a terminal. Examples of terminal emulators are:

  • The Terminal and iTerm applications in MacOS
  • The gnome-terminal, xterm and konsole applications in Linux
  • Putty and mintty for Windows.

Just as there are many terminal applications, there are also several shells. Examples of shells are:

  • The Bourne Shell (sh)
  • The Bourne Again Shell (bash)
  • The TC shell (tcsh)
  • The Z Shell (zsh)
  • The Debian Almquist Shell (dash)

A shell is more than just an interactive command interpreter. It is capable of also interpreting input from files (called shell scripts). A shell also provides a high-level programming language that can be used to specify complex tasks to operating system.

Logging into a shell

Open the terminal emulator application that is available in your computer. If you are using a MacOS or Linux system, the Terminal application will immediately create a shell session with your local operating system.

In this course, however, you are required to log into the host. To establish a remote session with “blue”, you will use the ssh command. The basic syntax for this command is ssh <username>@<host>, where username corresponds to your user and host to the name or IP address of the remote host. Type the following, substituting me with your username.

[jorge@localhost ~]$ ssh's password:
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.3-201.fc22.x86_64 x86_64)

 * Documentation:
Last login: Sat Jan 21 20:11:54 2017 from
[me@blue ~]$


You might be asked to confirm the authenticity of the host If you are connected to the University’s network, it is safe to accept by typing yes.

The welcome message might also be different from the example output.

The shell prompt

Notice that after launching the terminal emulator and after logging into a remote system, you get a short sequence of characters before the cursor. In the example above you can see the [jorge@localhost ~]$ prompt in the local shell and [me@blue ~]$ prompt in the remote shell. You do not have to type the prompt in the examples. The prompt is the way for the shell to tell you that it is ready to accept input. Prompts are customizable, and you will see later in this course that they can be very useful. In the example output, the prompt from lets you know that the user me is logged in the blue host and that the current working directory is ~ (We will go into the details of directories pretty soon).

Executing commands

You can enter an edit commands in the shell after the prompt. Once you have typed the command, you need to press ENTER to trigger the execution of the command. Try running the date command:

[me@blue ~]$ date
Sun Jan 22 00:10:43 UTC 2017

Notice how the shell wrote back to the screen the result of the command.

Commands can be entered by themselves, as the previous example. Most commands accept arguments when we need the command to perform an action with a certain input. For example, the echo command can be used to write text on the screen:

[me@blue ~]$ echo 'Hello World'
Hello World

Here echo is the command name (sometimes referred to as utility or program), and 'Hello World' is the argument.

Commands typically accept options (sometimes called flags) that modify the behavior of the command. For example, the -n option causes the echo command to not append a new line to the output:

[me@blue ~]$ echo -n 'Hello World'
Hello World[me@blue ~]$

Getting Help

You can obtain more information about commands by using the man utility. For example, to access the man page for the date command that we just executed:

[me@blue ~]$ man date

this will present a screen like this:


Scroll through the man page (by using the UP and DOWN keys, and see how the command’s syntax and options are explained in detail. To exit the man page type q, this will cause the session to return to the shell prompt.

Editing Efficiently

bash has several special key combinations that allow easy and fast command editing.

keys Function
LEFT and RIGHT Move the cursor in the command line
UP and DOWN Scroll through the command history
CTRL+a Move the cursor to the begining of the command line
CTRL+e Move the cursor to the end of the command line
META+f Move forward one word
META+b Move backward one word
CTRL+k Kill (delete) the text from cursor to the end of the line
CTRL+u Kill the text from cursor to the beginning of theline
META+d Kill the current word
META+r Undo all changes made to the line
CTRL+l Clear the screen
CTRL+r Search command history
TAB Command or filename completion


The META key is not included in most modern keyboard layouts, however, the ESC key is used to “metafy” the next typed character. We maintain the reference to the META key for consistency with official documentation.

To practice these shortcuts, we are going to use the curl command and python to use the shell and the internet for our entertainment. Type the following command (if you make any mistakes use the LEFT and RIGHT to move the cursor to the right place and use BACKSPACE to remove unwanted characters)

[me@blue ~]$ curl -s | python -m json.tool

That command should return one of things that I personally find most amusing from the internet: a random Chuck Norris joke. However, having to type all that is not fun and it takes a lot of time. Luckily for us, there is an easy way to get another random joke without little effort: press the UP one time, and press the ENTER key. Feel free to repeat this a few times.

One of my favorite Chuck Norris jokes is joke number 458. We can get a specific joke by replacing random with the joke number, as an example:

[me@blue ~]$ curl -s | python -m json.tool
    "type": "success",
    "value": {
        "categories": [
        "id": 458,
        "joke": "Chuck Norris can write infinite recursion functions and have them return."

Instead of typing everything again, try the following key strokes:

  • UP : recall the last command you ran
  • META-b : moves the cursor one word back. You will need to do this at least 8 times, until the cursor is locaded under the “r” key from “random”. Notice how words are identified in terms of spaces and special characters.
  • META-d : deletes the random word
  • 478: the joke that we want
  • ENTER: to read joke 458

Moving back word by word is definitely more eficient than one character at a time. However, we can move faster by moving to the especific place in the command that we want to edit. Joke 479 is pretty good too. Let’s see how we can get it quickly:

  • UP : recall the previous command
  • CTRL+r: enter reverse history search mode
  • 8: to position the cursor under the 9 character
  • LEFT: to exit reverse history search mode
  • BACKSPACE: to remove the 8 character
  • 9: to complete the joke number we want (459)
  • ENTER: to read joke 459

Exiting the shell

To exit a shell session, type :command:exit. Note that if you are connected to blue, when you execute the exit you will be back in your workstation’s shell session.


  1. What happens if you run the command echo -e 'Hello\nWorld'? What is the purpose of the -e option? What is the meaning of the \n in the command’s argument? What happens if you remove the single quotes that enclose the argument?
  2. What command can be used to print the system date in the UTC timezone?
  3. What is the purpose of the hostname command? What is the output when you execute this in blue? Compare this with the output when you are not connected to blue. What is effect of using the -i option with this command? Again, compare the output of running this command when executed in blue and when run locally.
  4. Execute the command echo Hello\nLinux. This prints the text HellonLinux` in a single line.  Provide a sequence of keystrokes that will cause the shell to print the word ``Hello in one line, and the word Linux on the next line.