Working with scripts and loops

 

Work with Variables

There will be several tasks that you need to perform repeatedly in penetration testing. Either you can keep doing them manually, or you can automate them using scripts. There is nothing wrong with doing things manually, except that you are spending more time in doing them. You are also likely to make more errors when you do them manually. On the other hand, if you use a script to perform a task, you are likely to get the same result without any error.

Scripts can be created in different languages, such as

• Bash: It is mostly used in Linux and Unix environments. Any operating system, which uses Linux as the base shell, can use Bash-based shell scripts. A bash script, or shell script, use the extension .sh.
• PowerShell: It is mostly used in the Windows environment. However, since it is an open-source tool, you can also use it on Linux and Mac operating systems. A PowerShell script has the .ps1 extension.
• Ruby: It is an interpreted language that is not limited to the operating system commands. You need to write a script and run it. There is no need to compile the script or code as you would need to do in C language. A Ruby script has the .rb extension.
• Python: Just like Ruby, Python is also an interpreted language. Python is used heavily in penetration testing because of its robustness. A Python script has the .py extension.

Note: In this module, you will largely focus on writing small scripts in Bash.

Depending upon the requirement and your expertise, you can use any of them in penetration testing.

Scripts are run in the shell environment in any operating system. When writing a script, you will use variables, which are mainly used for storing a type of data in memory and then use it later. Variables can store various types of information, such as:

• Integers
• Character strings
• Boolean
• Date and time

In this exercise, you will learn to work with variables.

Learning Outcomes

After completing this exercise, you will be able to:

• Use Local and Global Variables
• Write Bash Functions
• Use the Set Command

Your Devices

You will be using the following device in this lab. Please power on the device.

• PLABKALI01 - (Kali 2019.2 - Linux Kali)

Task 1 - Use Local and Global Variables

There can be two types of variables in Linux. The first variable is the local variable that is used within the current shell. The moment the shell is closed, the variable is removed and is no longer available. When you load a new shell within the current shell, the local variable is no longer available.

The global variable, on the other hand, is available across the shells. Even if you load a shell within the current shell, the global variable will be available.

To use local and global variables, perform the following steps:

Step 1

Ensure you have powered on all the devices listed in the introduction and connect to PLABKALI01.

On the PLABKALI01 desktop, click the Terminal icon.

Figure 1.1 Screenshot of PLABKALI01: Clicking the Terminal icon on the left pane.

Step 2

On the desktop, in the left pane, click the Terminal icon.

Figure 1.2 Screenshot of PLABKALI01: Clicking the Terminal icon in the left pane.

Step 3

The terminal window is displayed. Let’s first declare a local variable. To do this, type the following command in the terminal window:

plab=apple

Press Enter.

Figure 1.3 Screenshot of PLABKALI01: Declaring a local variable named plab.

Step 4

Notice that there is no output.

Figure 1.4 Screenshot of PLABKALI01: Showing the successful declaration of plab variable.

Step 5

You need to verify if the variable has been created with the value as the apple. Type the following command:

echo $plab

Press Enter.

Figure 1.5 Screenshot of PLABKALI01: Verifying if the variable has been created with the value as the apple.

Step 6

Notice that the output is displayed as the apple.

Figure 1.6 Screenshot of PLABKALI01: Showing the output of the echo command and its output.

Step 7

Remember that you have declared a local variable named plab. Its value is limited to the current shell. You can verify if the variable is available outside the current shell, and to do this, let’s open another child shell within the current shell. Type the following command:

/bin/bash

Press Enter.

Figure 1.7 Screenshot of PLABKALI01: Executing a command to create a child shell.

Step 8

The prompt will remain the same, but you are in a child shell.

Figure 1.8 Screenshot of PLABKALI01: Showing the prompt at the child shell.

Step 9

You can now verify for the plab variable. To do this, type the following command:

echo $plab

Press Enter.

Figure 1.9 Screenshot of PLABKALI01: Executing the echo command to display the value of plab variable.

Step 10

Notice that an empty line is printed. This means that the plab variable does not exist in this shell.

Figure 1.10 Screenshot of PLABKALI01: Showing no value for the plab variable.

Step 11

Let’s define the plab variable in the child shell with the value banana. To do this, type the following command:

plab=banana

Press Enter.

Figure 1.11 Screenshot of PLABKALI01: Defining the plab variable in the child shell.

Step 12

The variable plab is now defined with the value as the banana.

Figure 1.12 Screenshot of PLABKALI01: Showing that the plab variable is now defined.

Step 13

You need to verify if the variable has been created with the value as the banana. Type the following command:

echo $plab

Press Enter.

Figure 1.13 Screenshot of PLABKALI01: Verifying if the variable has been created with the value as the banana.

Step 14

Notice that the output is displayed as the banana. This means that you can create a local variable with the same name in different shells and store different values.

Figure 1.14 Screenshot of PLABKALI01: Showing the value of the plab variable.

Step 15

To exit from the child shell, type the following command:

exit

Press Enter.

Figure 1.15 Screenshot of PLABKALI01: Using the exit command to exit from the child shell.

Step 16

You are back on the shell that you had initially used to declare plab with the value apple. Type the following command:

echo $plab

Press Enter.

Step 17

Notice that the value is now shown as the apple.

Figure 1.17 Screenshot of PLABKALI01: Showing the value of the plab variable.

Step 18

Clear the screen by entering the following command:

clear

Next, you will focus on creating a global variable. The method of creating a global variable is the same as creating a local variable. However, you need to use the export command to set a local variable as global. Let’s verify the value of the local variable, plab, that you have already declared. Type the following command:

echo $plab

Press Enter.

Figure 1.18 Screenshot of PLABKALI01: Showing the value of the plab variable.

Step 19

Notice that the value is now shown as the apple.

Figure 1.19 Screenshot of PLABKALI01: Showing the value of the plab variable with the echo command.

Step 20

You now need to make plab a global variable. To do this, type the following command:

export plab

Press Enter.

Figure 1.20 Screenshot of PLABKALI01: Executing the export command to make plab a global variable.

Step 21

Notice that there is no output generated.

Figure 1.21 Screenshot of PLABKALI01: Showing the successful execution of the export command.

Step 22

You need to open a child shell. To do this, type the following command:

/bin/bash

Press Enter.

Figure 1.22 Screenshot of PLABKALI01: Creating a child shell within the current shell.

Step 23

You are now in the child shell.

Figure 1.23 Screenshot of PLABKALI01: Showing the prompt in the child shell.

Step 24

Let’s check the value of the plab variable. Type the following command:

echo $plab

Press Enter.

Figure 1.24 Screenshot of PLABKALI01: Checking the value of the plab variable in the child shell.

Step 25

Notice that the plab displays the output as the apple. Remember, you did not define any variable this time in the child shell, but you are able to get the value of the variable.

Figure 1.25 Screenshot of PLABKALI01: Showing the value of the plab global variable in the child shell.

Step 26

To exit from the child shell, type the following command:

exit

Press Enter.

Step 27

You are back on the shell that you had initially used to declare plab with the value apple.

echo $plab

Press Enter.

Figure 1.27 Screenshot of PLABKALI01: Checking the value of the plab variable in the parent shell.

Step 28

The plab variable still displays the value as the apple.

Figure 1.28 Screenshot of PLABKALI01: Showing the value of the plab variable in the parent shell.

Keep the terminal window open.

Task 2 - Write Bash Functions

You can use functions to trigger several commands. A function is a series of commands that can be executed by referring to the function name. Writing bash functions for the frequently used commands enables you to execute multiple commands by issuing one that calls the relevant bash function. You can use two methods to declare the bash functions.

Method 1

In this method, the function name is defined without any reserved word.

function_name () {
  commands
}

This method can also be written as:

function_name () { commands; }

Method 2

This method starts the function with the reserved word named function.

function function_name {

commands

}

This method can also be written as:

function function_name { commands; }

After the function name, with or without the reserved word, you need to use the {} to define the commands. The closing curly brace (}) closes the function. After defining a function, you need to call it by using its name.

In this task, you will write a bash function.

To write bash functions, perform the following steps:

Step 1

Clear the screen by entering the following command:

clear

To write a bash function, type the following commands:

function plab() { ls -l /etc; }

Press Enter.

Figure 1.29 Screenshot of PLABKALI01: Creating a function named plab.

Step 2

To run the function, type the following command:

plab

Press Enter.

Figure 1.30 Screenshot of PLABKALI01: Running the function named plab.

Step 3

The plab function displays the directory listing of the /etc directory.

Figure 1.31 Screenshot of PLABKALI01: Showing the output of the plab function.

Keep the terminal window open.

Task 3 - Use the Set Command

The set command is used to define and determine the values of the local system environment. To set the command search path with the proper directory, perform the following steps:

Step 1

Ensure you have powered on all the devices listed in the introduction and connect to PLABKALI01.

Clear the screen by entering the following command:

clear

You can use the set command to view the functions and variables currently being used by the shell. Type the following command:

set

Press Enter.

Figure 1.32 Screenshot of PLABKALI01: Entering the set command on the terminal.

Step 2

The output of the set command is displayed.

Figure 1.33 Screenshot of PLABKALI01: Viewing the functions and variables currently being used by the shell.

Step 3

Clear the screen by entering the following command:

clear

You can also set the path using the set command. Type the following command:

set PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games"

Press Enter.

Figure 1.34 Screenshot of PLABKALI01: Setting the path using the set command.

Step 4

Notice that there is no output generated. This means that the command has run successfully.

Figure 1.35 Screenshot of PLABKALI01: Showing the outcome of the set command.

Step 5

Clear the screen by entering the following command:

clear

You can display the path using the following command:

echo $PATH

Press Enter.

Figure 1.36 Screenshot of PLABKALI01: Showing the path using the echo command.

Step 6

The output of the echo $PATH command is displayed.

Figure 1.37 Screenshot of PLABKALI01: Showing the output of the echo $PATH command.

Step 7

Clear the screen by entering the following command:

clear

The unset command deletes the variables. Type the following command:

unset

Press Enter.

Figure 1.38 Screenshot of PLABKALI01: Entering the unset command in the terminal.

Step 8

Notice that no output has been generated.

Figure 1.39 Screenshot of PLABKALI01: Showing the output of the unset command.

Keep the terminal window open.

Work with Loops

The Bash-based shell script files are stored with an extension of .sh. Each script contains a script interpreter that appears as a commented line in the script. In this task, you will create and execute simple scripts to implement loops.

When writing shell scripts, you would need to build conditional statements. There are different conditional statements that are written with the help of different types of loops. You will also learn how to execute the loops without writing shell scripts.

In this exercise, you will learn about working with loops.

Learning Outcomes

After completing this exercise, you will be able to:

• Use the For loop
• Use If…Else statements
• Use the While Loop

Your Devices

You will be using the following device in this lab. Please power on the device.

• PLABKALI01 - (Kali 2019.2 - Linux Kali)

Task 1 - Use For Loop

Assume that you have to repeat a task several times. You can write the code several times with a bit of variation to arrive at a specific result, or you can use loops to get the desired output. The for loop runs through a list of values in a list until the time list values are exhausted.

In this task, you will learn to use loops. To do this, perform the following steps:

Step 1

Clear the screen by entering the following command:

clear

Note: The clear command is used before every step to enable the learners to get a clear view of the output of each command. Otherwise, it is not mandatory to use the clear command before every command.

You can create a script using the vi editor or any other editor that is available in Kali Linux.

To create a script, type the following command:

vi plab.sh

Press Enter.

Figure 2.1 Screenshot of PLABKALI01: Creating a script using the vi command.

Step 2

The vi editor is displayed.

Figure 2.2 Screenshot of PLABKALI01: Displaying the vi editor window.

Step 3

Before you type anything in the vi editor, you need to start the insert mode. Press i to invoke the insert mode.

Notice that the INSERT word appears at the bottom. This indicates that the vi editor is now in the insert mode.

Figure 2.3 Screenshot of PLABKALI01: Entering the insert mode in the vi editor.

Step 4

While creating a script, you need first to define the script interpreter. The commonly used interpreters include bash or sh, although other interpreters are available.

For this task, you specify bash as the script interpreter. Type the following command:

#!/bin/bash

Press Enter.

Figure 2.4 Screenshot of PLABKALI01: Defining the script interpreter.

Step 5

In the next line, type the following command:

ls -l

Press Enter.

Figure 2.5 Screenshot of PLABKALI01: Entering the script statements.

Step 6

Now, you need to save the file.

To save and close the file, press ESC and then type the following command:

:wq

Press Enter.

Figure 2.6 Screenshot of PLABKALI01: Saving and closing the file.

Step 7

You are back on the command prompt.

Figure 2.7 Screenshot of PLABKALI01: Displaying the command prompt.

Step 8

To verify that the script is created, type the following command:

ls

Press Enter.

Notice that the plab.sh file is listed in the root directory.

Figure 2.9 Screenshot of PLABKALI01: Showing the list of files in the root directory.

Step 10

Clear the screen by entering the following command:

clear

To run the bash scripts, type the following command:

bash plab.sh

Press Enter.

Figure 2.10 Screenshot of PLABKALI01: Executing the plab.sh file with the bash command.

Step 11

Note that the script runs successfully.

Figure 2.11 Screenshot of PLABKALI01: Showing the output of the bash.sh script.

Step 12

The scripts with executable permissions can be run by prefixing the ./ with their names. For example, to execute plab.sh without the help of bash, you can enter ./plab.sh

To run plab.sh, type the following command:

 ./plab.sh

Press Enter.

Figure 2.12 Screenshot of PLABKALI01: Executing the bash.sh script using ./.

Step 13

Note that there is an error that states permission is denied to run this shell script.

Figure 2.13 Screenshot of PLABKALI01: Displaying the error after executing the script.

Step 14

Let’s now change the permissions on the scripts to allow everyone to execute this script. To add permissions, type the following command:

chmod 777 plab.sh

Press Enter.

Figure 2.14 Screenshot of PLABKALI01: Changing the permission on the script using the chmod command.

Step 15

Notice that there is no output of this command.

Figure 2.15 Screenshot of PLABKALI01: Showing the command prompt after the chmod command.

Step 16

Clear the screen by entering the following command:

clear

To run the plab.sh script, type the following command:

./plab.sh

Press Enter.

Figure 2.16 Screenshot of PLABKALI01: Executing the bash.sh script using ./.

Step 17

Notice that the script is running now.

Figure 2.17 Screenshot of PLABKALI01: Showing the output of the plab.sh script.

Step 18

Clear the screen by entering the following command:

clear

You can also create a script to execute a loop. For example, you can write a script to create 10 users without having to enter the useradd command 10 times. You will use the for loop to do this.

To use the vi editor to create a new script with the name plabuser.sh, type the following command:

vi plabuser.sh

Press Enter.

Figure 2.18 Screenshot of PLABKALI01: Creating a script named plabuser.sh using the vi editor.

Step 19

The vi editor is displayed.

Figure 2.19 Screenshot of PLABKALI01: Displaying the vi editor.

Step 20

Press i to invoke the insert mode.

Figure 2.20 Screenshot of PLABKALI01: Entering the insert mode.

Step 21

To specify the script interpreter, type the following command:

#!/bin/bash

Press Enter.

After that, type the following lines:

for u in $(seq 10); do
useradd user$u
echo user${u}
done

This script creates 10 users with the names starting with user1, user1, and so on.

Figure 2.21 Screenshot of PLABKALI01: Entering the statements in the script.

Step 22

Now, you need to save and close the file. To save the file, press ESC and then type the following command:

:wq

Press Enter.

Figure 2.22 Screenshot of PLABKALI01: Saving and exiting the file.

Step 23

You are back on the command prompt.

Figure 2.23 Screenshot of PLABKALI01: Displaying the command prompt.

Step 24

To execute the plabuser.sh script, you change the permissions given to the script.

To change permissions, type the following command:

chmod 777 plabuser.sh

Press Enter.

Figure 2.24 Screenshot of PLABKALI01: Changing the script permissions.

Step 25

Notice that there is no output of this command.

Figure 2.25 Screenshot of PLABKALI01: Showing the prompt in the terminal.

Step 26

Now, to run the script, type the following command:

./plabuser.sh

Press Enter.

Figure 2.26 Screenshot of PLABKALI01: Executing the plabuser.sh script using ./.

Step 27

Note that 10 users have been created.

Figure 2.27 Screenshot of PLABKALI01: Showing the output of the plabuser.sh script.

Keep the terminal window open.

Task 2 - Use If…Else statements

The if…else statements are mainly used for making a decision and, therefore, are known as decision-making statements. However, there may be a scenario in which you will have to work with multiple conditions to choose from, then how to use the case…ecac statements.

In this task, you will learn to use if…else statements. To use the if…else statements, perform the following steps:

Step 1

Ensure you have powered on all the devices listed in the introduction and connect to PLABKALI01.

Clear the screen by entering the following command:

clear

In shell scripting, you can use three different types of if…else statements. They are the following:

• if...fi statement
• if...else...fi statement
• if...elif...else...fi statement

Let’s first create a new shell script in which you will compare two values of x and z and accordingly display the result. Type the following command to create a new file:

gedit if_fi.sh

Press Enter.

Figure 2.28 Screenshot of PLABKALI01: Opening a new file in gedit.

Step 2

Notice a new file is created with the name if_fi.sh. Type the following:

#!/bin/sh
x=10
z=20
if [ $x = $z ]
then
   echo "x is same as z"
elif [ $x -gt $z ]
then
   echo "x is more than z"
elif [ $x -lt $z ]
then
   echo "x is less than z"
else
   echo "None of them match"
fi

Figure 2.29 Screenshot of PLABKALI01: Entering the statements in the file.

Step 3

Click Save to save the file. Then, close the file.

Figure 2.30 Screenshot of PLABKALI01: Saving and closing the file.

Step 4

Clear the screen by entering the following command:

clear

You need to make the shell script executable. Type the following command:

chmod 777 if_fi.sh

Press Enter.

Figure 2.31 Screenshot of PLABKALI01: Making the file executable using the chmod command.

Step 5

Notice that no output is displayed after the command execution. You will now execute the shell script. Type the following command:

./if_fi.sh

Press Enter.

Figure 2.32 Screenshot of PLABKALI01: Executing the if_fi.sh script using ./.

Step 6

Note that the last condition is met in which x is less than z.

Figure 2.33 Screenshot of PLABKALI01: Showing the output of the if_fi.sh script.

Step 7

Clear the screen by entering the following command:

clear

In a scenario where you have multiple conditions, it is best to use case…esac statements. Create a new file with gedit, and name is case.sh. Type the following command:

gedit case.sh

Press Enter.

Figure 2.34 Screenshot of PLABKALI01: Creating a new script using the gedit command.

Step 8

A new file case.sh is displayed. Type the following:

#!/bin/sh
CAR="Honda"
case "$CAR" in
   "Ferrari") echo "Ferrari is quite expe    nsive."
   ;;
   "Jaguar") echo "I like Jaguar."
   ;;
   "Honda") echo "Honda is the car of the year."
   ;;
esac

Figure 2.35 Screenshot of PLABKALI01: Entering the statements in the new file.

Step 9

Click Save to save the file. Then, close the file.

Figure 2.36 Screenshot of PLABKALI01: Saving and closing the file.

Step 10

Clear the screen by entering the following command:

clear

You need to make the shell script executable. Type the following command:

chmod 777 case.sh

Press Enter.

Figure 2.37 Screenshot of PLABKALI01: Changing the permissions of the script.

Step 11

Notice that no output is displayed.

Figure 2.38 Screenshot of PLABKALI01: Showing the prompt in the terminal window.

Step 12

Clear the screen by entering the following command:

clear

You will now execute the shell script. Type the following command:

./case.sh

Press Enter.

Figure 2.39 Screenshot of PLABKALI01: Executing the case.sh script with ./.

Step 13

Notice the answer. After evaluating two conditions, the third condition meets the criteria and is printed as the answer.

Figure 2.40 Screenshot of PLABKALI01: Showing the of the case.sh script.

Keep the terminal window open.

Task 3 - Use While Loop

A while loop runs until a statement becomes true. It can nest other loops. There is no limit to nesting loops. The number is limited to your requirement. In this task, you will learn to use while loop. To use the loop, perform the following steps:

Step 1

Ensure you have powered on all the devices listed in the introduction and connect to PLABKALI01. Clear the screen by entering the following command:

clear

Let’s first create a new shell script with the following command:

gedit while.sh

Press Enter.

Figure 2.41 Screenshot of PLABKALI01: Opening a new file in gedit.

Step 2

Notice a new file is created with the name while.sh. Type the following:

#!/bin/bash
a=0
while [ $a -le 10 ]
do
  echo "Welcome $a times."
  a=$(( a+1 ))  
done

Note: the spaces before the lines "echo " and "A=$" is made by pressing the TAB button

Figure 2.42 Screenshot of PLABKALI01: Entering the statements in the file.

Step 3

Click Save to save the file. Then, close the file.

Figure 2.43 Screenshot of PLABKALI01: Saving and closing the file.

Step 4

Clear the screen by entering the following command:

clear

You need to make the shell script executable. Type the following command:

chmod 777 while.sh

Press Enter.

Figure 2.44 Screenshot of PLABKALI01: Making the file executable using the chmod command.

Step 5

Clear the screen by entering the following command:

clear

You will now execute the shell script. Type the following command:

./while.sh

Press Enter.

Figure 2.45 Screenshot of PLABKALI01: Executing the while.sh script using ./.

Step 6

Note that Welcome has been printed 11 times, starting from 0 to 10. This condition was defined in the while loop.

Figure 2.46 Screenshot of PLABKALI01: Showing the output of the while.sh script.

Keep the terminal window open.

Use Error Handling and Arrays

One of the common methods is to insert and unexpected input that can generate an error condition. Therefore, to avoid such a situation, developers should use the error-handling methods. Bash provides an alternate method instead of try…catch clause.

In this exercise, you will learn about error handling and arrays.

Learning Outcomes

After completing this exercise, you will be able to:

• Use Error Handling
• Use Arrays

Your Devices

You will be using the following device in this lab. Please power on the device.

• PLABKALI01 - (Kali 2019.2 - Linux Kali)

Task 1 - Use Error Handling

Many programming languages use the try…catch clause to handle errors. However, if you are using Bash to write shell scripts, then you will not be able to use try…catch clause. Instead, you can use && or ||. The && operator is the AND operator, which requires both the expressions in the command to be true. The first expression is a command, which must run for the second command to run. If the first command fails, the second command will not run.

The || operator is the OR operator. In this case, if the first command fails, then only the second command runs.

To learn about error handling, perform the following steps:

Step 1

Clear the screen by entering the following command:

clear

Let’s first try the AND operator. Remember, the first command must run for the second command to run. If the first command fails, then the second command will not run.

Type the following command:

cd test && touch plab.txt

Press Enter.

Figure 3.1 Screenshot of PLABKALI01: Executing a command with the AND operator.

Step 2

Notice the output of this command. There is no directory named test, and therefore, the first command fails. Since you are using the AND operator, the second command does not execute.

Figure 3.2 Screenshot of PLABKALI01: Showing the output of commands with the AND operator.

Step 3

Clear the screen by entering the following command:

clear

Let’s try the OR operator. Type the following command:

Type the following command:

cd test || touch plab.txt

Press Enter.

Figure 3.3 Screenshot of PLABKALI01: Executing the commands with the OR operator.

Step 4

Notice that the first command fails in this scenario. However, the second should have executed and created the plab.txt file.

Figure 3.4 Screenshot of PLABKALI01: Showing the output of commands with the OR operator.

Step 5

Let’s verify if the plab.txt file has been created with the touch command. To do this, type the following command:

ls -l

Press Enter.

Figure 3.5 Screenshot of PLABKALI01: Executing the ls command to list files.

Step 6

Notice that the plab.txt file is present in the current directory.

Figure 3.6 Screenshot of PLABKALI01: Showing the output of the ls command.

Keep the terminal window open.

Task 2 - Use Arrays

An array is a variable that can contain multiple values, which can be of the same or different types. Arrays do not have a size limit. Bash arrays use numbered indexes, and index starts with zero.

In this task, you will learn to use arrays. To do this, perform the following steps:

Step 1

Clear the screen by entering the following command:

clear

Let’s first create a shell script with an array.

Type the following command:

gedit array.sh

Press Enter.

Figure 3.7 Screenshot of PLABKALI01: Creating a script named array.sh using gedit.

Step 2

Notice a new file with the name array.sh is displayed. Type the following statements:

Note: An array is created automatically when you define a variable in the following format: name[index]=value

#!/bin/bash
Car[0]='Honda'
Car[1]='Ferrari'
Car[2]='Toyota'
Car[3]='Nissan'
echo ${Car[1]}

You will display the value of index 1.

Figure 3.8 Screenshot of PLABKALI01: Entering the statements in the array.sh script.

Step 3

Click Save to save the file. Then, close the file.

Figure 3.9 Screenshot of PLABKALI01: Saving and closing the file.

Step 4

Clear the screen by entering the following command:

clear

You need to make the shell script executable. Type the following command:

chmod 777 array.sh

Press Enter.

Figure 3.10 Screenshot of PLABKALI01: Making the file executable using the chmod command.

Step 5

Notice that no output is displayed after the command execution. You will now execute the shell script. Type the following command:

./array.sh

Press Enter.

Figure 3.11 Screenshot of PLABKALI01: Executing the script.

Step 6

Notice the outcome of the script that you run. The array runs successfully and generates the outcome.

Figure 3.12 Screenshot of PLABKALI01: Showing the output of the script.

Keep all devices that you have powered on in their current state and proceed to the review section.