Understanding and Using the "line" Command (with examples)

Introduction

In this article, we will explore the various use cases of the “line” command, which allows us to read a single line of input. We will discuss the different scenarios where this command can be useful, provide example code, explain each argument, and showcase the example output for better understanding.

1: Reading Input

Code:

line

Motivation:

The “line” command is useful when you need to read user input from the command line. It allows you to prompt the user for information without the need for complex scripting or programming.

Explanation:

The “line” command reads a single line of input from the user and stores it in a convenient shell variable named line. It waits for the user to provide input and press the enter key.

Example Output:

Enter your name: John Doe

2: Reading Input with Prompt

Code:

line "Enter your age: "

Motivation:

Sometimes, it is helpful to provide a prompt along with the input request to guide the user on what kind of input is expected. This can make the user interaction more intuitive and error-free.

Explanation:

The “line” command allows you to pass a prompt as an argument, which will be displayed before the user input request. This prompt can be a message or a question to guide the user.

Example Output:

Enter your age: 25

3: Reading Input with Default Value

Code:

line "Is it raining? [Y/n] " 'Y'

Motivation:

In some cases, it is helpful to provide a default value for user input to save time and effort. This can be particularly useful when the default value is commonly chosen by most users and provides a good starting point.

Explanation:

The “line” command allows you to specify a default value as the second argument. If the user provides no input and presses enter, the default value will be used instead.

Example Output:

Is it raining? [Y/n] 

(Default value ‘Y’ is automatically selected after pressing enter without any input)

4: Storing Input in a Custom Variable

Code:

line -p "Please enter your email address: " -v email

Motivation:

In some situations, it is necessary to store the user input in a custom shell variable rather than the default line variable. This gives you more flexibility in handling and manipulating the user input.

Explanation:

The “line” command allows you to use the -v option followed by a variable name to store the input into a custom variable. Instead of using the default line variable to store the input, you can access it later using the specified variable name.

Example Output:

Please enter your email address: example@example.com

(The input “example@example.com ” is stored in the email variable)

5: Reading Password Input

Code:

line -s "Enter your password: "

Motivation:

When dealing with sensitive information like passwords, it is crucial to hide the user input to avoid exposing it. The “line” command provides an option to read password input securely.

Explanation:

The -s option of the “line” command hides the typed characters, providing a secure way to read passwords. Instead of displaying the entered characters on the screen, they are masked to protect sensitive information.

Example Output:

Enter your password: ******

Conclusion

The “line” command is a versatile tool that allows you to read user input in various scenarios. Whether you need a simple input request or additional options like prompts, default values, custom variable storage, or secure password input, the “line” command has got you covered. By understanding and utilizing the different features of the “line” command, you can enhance the interactivity and usability of your command-line applications.