CompTIA Linux+ XK0-005 - 3.1 - Shell Script Elements - Built-in Commands: read

In shell scripting, the read command is a built-in command that allows you to read input from the user or from a file. It is a versatile command that enables interactive script execution and user interaction. Understanding how to use the read command is essential for creating dynamic and user-friendly shell scripts. In this guide, we will explore the read command and its various applications.

Using the read Command

The basic syntax of the read command is as follows:

read [options] variable

options: Additional options that modify the behavior of the read command. We will cover some commonly used options later in this guide.
variable: The name of the variable that will store the input value read by the read command.

Reading User Input

One common use case for the read command is to prompt the user for input during script execution. Here's an example:

#!/bin/bash

echo "Enter your name:"
read name

echo "Hello, $name! Welcome to the script."

In this example, the read command prompts the user to enter their name, and the value is stored in the name variable. The script then greets the user using the entered name.

Handling Multiple Inputs

You can use multiple read commands to prompt the user for different inputs. Here's an example:

#!/bin/bash

read -p "Enter your name: " name
read -p "Enter your age: " age

echo "Hello, $name! You are $age years old."

In this script, we use the -p option to provide a prompt message for each input. The values entered by the user are stored in the respective variables (name and age), and the script displays a personalized message using these values.

Reading Input from a File

The read command can also read input from a file. This is useful when you want to process data from a file within a script. Here's an example:

#!/bin/bash

filename="data.txt"

while read -r line
do
    echo "Processing: $line"
    # Add your processing logic here
done < "$filename"

In this example, the read command reads each line from the data.txt file and stores it in the line variable. You can then perform any required processing on each line within the loop.

Additional Options

The read command provides various options to customize its behavior. Here are a few commonly used options:

-p: Specifies a prompt message to be displayed before reading input.
-s: Makes the input silent, without displaying it on the screen (useful for password input).
-t: Sets a timeout for input, after which the read command exits if no input is provided.
-a: Reads input into an array variable.

Consult the documentation or man page for the read command to explore more options and their usage.

Conclusion

The read command is a versatile tool in shell scripting that allows you to interact with users, read input from files, and create dynamic and interactive scripts. By incorporating the read command into your scripts, you can prompt users for input, process data from files, and create engaging user experiences.

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