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Mastering BASH Scripting: Automating Tasks & Inputs from Console and Files

Introduction to BASH scripting

BASH scripting is a powerful tool that can help automate repetitive tasks and save time. BASH is a popular shell program that is used in Unix and Linux-based operating systems.

The term “BASH” stands for Bourne Again Shell, and it is an enhanced version of the Bourne Shell, which was developed in the 1970s. One of the primary bene

fits of using BASH scripting is that it allows you to automate tasks that would otherwise require manual intervention.

This can save a signi

ficant amount of time and effort, especially for tasks that need to be performed regularly. BASH scripting also provides an effective means of imperative programming, which makes it easier to create

readable and reusable code.

In this article, we will explore the fundamentals of BASH scripting, including its structure and syntax, as well as how to create and run BASH scripts.

Advantages of BASH scripting

BASH scripting has several advantages that make it a popular choice over other scripting languages. One of the most signi

ficant bene

fits is its ability to automate repetitive tasks.

With BASH scripting, you can write code that automates a wide range of tasks, such as

file management, data processing, and system administration. Another advantage of BASH scripting is its simplicity.

BASH uses a straightforward syntax that is easy to learn and understand, even for beginners. This makes it an accessible language for programmers and non-programmers alike.

Additionally, BASH scripting is highly customizable, which allows you to create scripts that will work with your speci

fic needs. With the help of BASH scripting, you can set up a system that automates tasks that would otherwise require manual intervention, thereby freeing up your time to focus on other things.

Creating a BASH script

To create a BASH script, you need to understand its structure and syntax.

Structure of a BASH script

A BASH script is a plain text

file that contains a sequence of instructions that are executed by the BASH interpreter. Scripts are typically given a .sh extension to indicate that they are BASH scripts.

Starting a BASH script with shebang

The

first line of a BASH script is commonly referred to as the shebang. This line tells the operating system which program to use to interpret the script.

Generally, the shebang line in a script will look like this:

#!/bin/bash

Here, the #! symbol is called a “hash-bang” or “shebang.” The /bin/bash part of the line speci

fies that the script should be executed by the Bash shell.

Running a BASH script

To run a BASH script, you need to call it using the bash command. This can be done by navigating to the directory containing the script and typing the following command:

$ bash scriptname.sh

Alternatively, you can make the script executable and run it directly.

To do this, you need to change the

file’s permissions using the chmod command. You can make a script executable by running this command:

$ chmod +x scriptname.sh

This command changes the

file permissions to make the script executable.

Once the script is executable, you can run it by typing:

$ ./scriptname.sh

Conclusion

BASH scripting is a useful tool that allows you to automate tasks and save time. By using the simple syntax of BASH, you can create scripts that perform a wide range of tasks, from data processing to system administration.

With the help of the information provided in this article, you should now have a basic understanding of BASH scripting, including how to structure a BASH script, the shebang line, and how to run a BASH script. With this knowledge, you are well on your way to becoming pro

ficient in BASH scripting.

3) Input from stdin in BASH script

BASH scripting provides various ways to accept user input from standard input (stdin). This input can be used to control the behavior of the script or to perform certain actions.

In this section, we will explore how to

read user input from the console with

read command, how to save multiple values in separate variables, how to use default variable REPLY, how to

read single-line input with the -p flag, how to

read hidden input with the -s flag, and how to

read an array with the -a flag.

Reading user input with

read command

The

read command is commonly used to

read input from the console in a BASH script. When executed,

read prompts the user to enter input and then stores that input in a variable.

Here is a basic example:

“`

#!/bin/bash

echo “What is your name?”

read name

echo “Hello, $name! Welcome

to BASH scripting.”

“`

In this example, the user is prompted to enter their name, and the value they enter is stored in the variable named “name.” After the user enters their name, the script displays a welcome message that includes the entered name.

Saving multiple values in separate variables

If the user needs to enter multiple values, separated by spaces, you can save them in separate variables by specifying the variable names after the

read command as shown below:

“`

#!/bin/bash

echo “Enter your

first name, last name, and age separated by spaces:”

read

first last age

echo “Hello, $

first $last! You are $age years old.”

“`

In this example, the user is prompted to enter their

first name, last name, and age, separated by spaces. The entered values are then stored in the variables “

first,” “last,” and “age,” respectively.

Using default variable REPLY

If you do not specify a variable name after the

read command, BASH uses the default variable REPLY to store the entered value. Here is an example:

“`

#!/bin/bash

echo “Enter your favorite color:”

read

echo “Your favorite color is $REPLY.”

“`

In this example, the user is prompted to enter their favorite color. Since no variable name is speci

fied after the

read command, the entered value is stored in the default variable REPLY.

Reading input with -p flag

The -p flag can be used to specify a prompt message for input. Using this flag eliminates the need for an echo statement in the script.

Here is an example:

“`

#!/bin/bash

read -p “Enter your age: ” age

if [ $age -lt 18 ]; then

echo “Sorry, you are not old enough to vote.”

else

echo “Great! You are old enough to vote.”

fi

“`

In this example, the -p flag is used to prompt the user to enter their age, eliminating the need for an echo statement. The entered age is then used to determine whether or not the user is old enough to vote.

Reading input silently with -s flag

The -s flag can be used to

read input silently. This is useful for

reading passwords or other sensitive information from the user.

Here is an example:

“`

#!/bin/bash

read -s -p “Enter your password: ” password

echo “Password accepted.”

“`

In this example, the -s flag is used to

read the password silently, so it is not visible on the console. The entered password is then processed without being displayed to the user.

Reading input in an array with -a flag

The -a flag can be used to

read input into an array variable. This is useful for processing multiple inputs that are related to each other.

Here is an example:

“`

#!/bin/bash

read -a numbers -p “Enter three numbers separated by spaces: “

echo “You entered ${numbers[0]}, ${numbers[1]}, and ${numbers[2]}.”

“`

In this example, the -a flag is used to

read the entered values into an array variable named “numbers.” The script then displays the entered values by accessing them using their index values. 4) Bash

file input

BASH scripts can also

read input from

files.

In this section, we will explore how to

read input from a

file using the

read command, how to

read input from a

file with a BASH script, and how to

read a

filename from the command line. Reading from a

file with

read command

The

read command can also be used to

read input from a

file.

This is useful for processing

files that have a speci

fic format. Here is an example:

“`

#!/bin/bash

filename=”data.txt”

while

read line

do

echo $line

done < $

filename

“`

In this example, the

read command is used to

read the

file “data.txt” line by line. The while loop is used to

read each line and display it on the console.

Reading from a

file with a BASH script

You can also

read input from a

file in a BASH script by using redirection. Redirection allows you to redirect the standard input or output of a command or script to a different

file or device.

Here is an example:

“`

#!/bin/bash

filename=”data.txt”

while

read line

do

echo $line

done < $

filename

“`

In this example, the script

reads input from the

file “data.txt” using the while loop and the

read command. The script will continue to

read each line in the

file until it reaches the end of the

file.

Reading

file name from command line

You can

read a

filename from the command line by using the

first argument value. Here is an example:

“`

#!/bin/bash

filename=$1

while

read line

do

echo $line

done < $

filename

“`

In this example, the script

reads the

filename from the

first argument using the variable $1. The script then uses the while loop and the

read command to

read input from the

file and displays each line on the console.

Conclusion

BASH scripting is a versatile tool that can be used to automate tasks and process information. By using different input methods, you can create more sophisticated and useful scripts.

In this article, we explored different techniques for

reading input from the console and from

files, including how to

read multiple values, prompt messages, and arrays. We also discussed how to

read

filenames from the command line, enabling us to be more flexible in our use of BASH scripts.

I hope this article has helped you to better understand BASH scripting and how to use it effectively. In summary, BASH scripting is a powerful tool that can automate repetitive tasks, making it an ef

ficient means of imperative programming.

This article explored the basics of BASH scripting, including its structure, syntax, and how to create and run BASH scripts. Moreover, it delved into

reading user input and

file input in the form of single-line, hidden, and array input.

Lastly, BASH scripts can

read

filenames from the command line too. Overall, learning BASH scripting can be advantageous and time-saving.

By applying the concepts discussed in this article, one can create scripts that perform various tasks and processes, thereby increasing their productivity.

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