Linux Text Display

Introduction

In this lab, you will learn how to display text in the Linux terminal using basic commands. The primary focus will be on the echo command, which is a fundamental tool used to display messages, show command results, and create simple text files.

Understanding how to display text is essential for any Linux user. It helps in creating scripts, viewing information, and communicating with the system. This lab will guide you through using the echo command in various ways, from simple text output to more complex uses with variables and redirection.

By the end of this lab, you will be comfortable using the echo command and understand its importance in the Linux environment.

Skills Graph

Basic Text Display with Echo

The echo command is one of the most commonly used commands in Linux. Its primary function is to display text or the value of a variable to the standard output (usually your terminal screen).

Using the Echo Command

In this step, you will learn the most basic usage of the echo command - displaying a simple text message.

Open your terminal and make sure you are in the home directory. You can check your current location using the pwd command:

pwd

You should see output similar to:

/home/labex/project

Now, let's use the echo command to display a simple message:

echo "Hello, Linux World"

After running this command, you should see the following output in your terminal:

Hello, Linux World

The echo command simply displays whatever text you provide between the quotation marks. This is the most basic form of the command, but it's incredibly useful for scripts, debugging, and providing user feedback.

Try displaying a different message:

echo "Learning Linux commands is fun"

Output:

Learning Linux commands is fun

Why Use Echo?

The echo command is versatile and can be used to:

• Display messages to users
• Show the values of variables
• Create simple text files
• Debug scripts by showing the values of variables or the progress of a script

In the next steps, we will explore more advanced uses of the echo command.

Working with Paths and Command Substitution

In this step, you will learn how to use the echo command with command substitution to display the output of other commands.

Command Substitution in Echo

Command substitution allows you to replace a command with its output. This is done using the syntax $(command). When the shell encounters this structure, it executes the command inside the parentheses and replaces the entire $(command) with the output of the command.

Let's use command substitution to display your current working directory:

echo "Current directory: $(pwd)"

When you run this command, you should see output similar to:

Current directory: /home/labex/project

In this example, $(pwd) is replaced with the output of the pwd command, which displays your current working directory.

Saving Output to a File

You can also redirect the output of the echo command to a file instead of displaying it on the screen. This is done using the redirection operator >.

Let's create a file called path_info.txt in your project directory that contains information about your current location:

cd ~/project
echo "Current path: $(pwd)" > path_info.txt

This command will create a file named path_info.txt in your project directory with the content "Current path: /home/labex/project" (or whatever your current path is).

To verify the content of the file, you can use the cat command:

cat path_info.txt

You should see output similar to:

Current path: /home/labex/project

The > operator redirects the output of the echo command to the specified file. If the file already exists, it will be overwritten. If you want to append to an existing file instead of overwriting it, you can use the >> operator.

For example, let's add the date and time to our file:

echo "Current date and time: $(date)" >> path_info.txt

Now check the content of the file again:

cat path_info.txt

You should see both lines:

Current path: /home/labex/project
Current date and time: Wed Jan 5 10:15:30 UTC 2023

(The actual date and time will reflect your system's current date and time.)

Echo with Formatting Options

In this step, you will learn how to use various options with the echo command to control the formatting of the output.

Using the -n Option

By default, the echo command adds a newline character at the end of its output. This is why each echo command's output appears on a new line. The -n option prevents this behavior.

Try the following commands:

echo "First line"
echo "Second line"

Output:

First line
Second line

Now try using the -n option:

echo -n "First line "
echo "Second line"

Output:

First line Second line

Notice how "Second line" appears on the same line as "First line" because we used the -n option with the first echo command.

Using the -e Option

The -e option enables the interpretation of backslash escapes. This allows you to include special characters in your output.

Some commonly used escape sequences include:

• \n - Newline
• \t - Tab
• \b - Backspace
• \\ - Backslash
• \" - Double quote

Let's try using the -e option with some escape sequences:

echo -e "Line 1\nLine 2"

Output:

Line 1
Line 2

Try using tabs:

echo -e "Name:\tJohn\nAge:\t30"

Output:

Name:	John
Age:	30

Combining Options

You can also combine options. For example, let's use both -n and -e:

echo -ne "Loading.\r"
sleep 1
echo -ne "Loading..\r"
sleep 1
echo -ne "Loading...\r"
sleep 1
echo -e "Done!     "

This simulates a simple loading animation. The \r escape sequence returns the cursor to the beginning of the line, allowing you to overwrite the previous output.

Creating a Formatted File

Let's create a file with formatted text:

cd ~/project
echo -e "User Information\n----------------\nUsername:\t$(whoami)\nHome Directory:\t$HOME\nCurrent Directory:\t$(pwd)" > formatted_info.txt

Check the content of the file:

cat formatted_info.txt

You should see a nicely formatted output similar to:

User Information
----------------
Username:	labex
Home Directory:	/home/labex
Current Directory:	/home/labex/project

In this example, we've used tabs (\t) to align the information and newlines (\n) to separate the lines.

Creating and Running a Simple Echo Script

In this step, you will learn how to create and run a simple shell script that uses the echo command. This will help you understand how echo is used in shell scripts, which are commonly used for automation in Linux.

What is a Shell Script?

A shell script is a file containing a series of commands that the shell can execute. Scripts allow you to automate tasks that would otherwise require typing multiple commands manually.

Creating the Script

You will now create a simple script that displays information about your system using the echo command. Follow these steps:

1. Open the file greeting.sh that was created in the setup phase:

cd ~/project
nano greeting.sh

2. Add the following content to the file:

#!/bin/bash

## This is a simple script that displays system information

echo "Welcome to the System Information Script"
echo "--------------------------------------"
echo "Current User: $(whoami)"
echo "Hostname: $(hostname)"
echo "Current Directory: $(pwd)"
echo "Date and Time: $(date)"
echo "--------------------------------------"
echo "Thank you for using this script!"

3. Save the file by pressing Ctrl+O, then press Enter. Exit nano by pressing Ctrl+X.

4. Make the script executable:

chmod +x greeting.sh

Running the Script

Now that you have created the script and made it executable, you can run it:

./greeting.sh

You should see output similar to:

Welcome to the System Information Script
--------------------------------------
Current User: labex
Hostname: labex
Current Directory: /home/labex/project
Date and Time: Wed Jan 5 10:30:45 UTC 2023
--------------------------------------
Thank you for using this script!

Understanding the Script

Let's break down what the script does:

1. The first line #!/bin/bash (called the shebang) tells the system which interpreter to use to execute the script. In this case, it's Bash.

2. Lines starting with # are comments and are ignored by the shell. They are useful for explaining what the script does.

3. The script uses several echo commands to display information:

   • Simple text strings: "Welcome to the System Information Script"
   • Command substitution: "Current User: $(whoami)" where $(whoami) is replaced with the output of the whoami command

Modifying the Script

Try modifying the script to include additional information. For example, you could add:

echo "Kernel Version: $(uname -r)"

Edit the script again:

nano greeting.sh

Add the new line before the "Thank you" message, save the file, and run it again.

This exercise demonstrates how the echo command is essential for providing feedback and displaying information in shell scripts.

Summary

In this lab, you learned how to use the echo command, one of the most fundamental commands in Linux for displaying text. Here's a recap of what you accomplished:

1. You learned the basic usage of the echo command to display simple text messages in the terminal.

2. You explored how to use command substitution with echo to include the output of other commands in your text, and how to redirect the output to files.

3. You discovered how to use formatting options with echo, including the -n option to prevent newlines and the -e option to interpret escape sequences.

4. You created a shell script that uses multiple echo commands to display system information, demonstrating how echo is used in script development.

These skills are essential for many Linux operations, including:

• Script development and debugging
• User interface creation in command-line applications
• System administration tasks
• Creating configuration files
• Providing user feedback in automated processes

As you continue your Linux journey, you'll find the echo command to be an invaluable tool for a wide range of tasks. It's often used in combination with other commands and shell features to create powerful and informative scripts.