Example of scripts and solution

Practice Exercises:

Exercise 1:

Write a shell script that prints "Shell Scripting is Fun!" on the screen.

Hint 1:  Remember to make the shell script executable with the chmod command.

Hint 2:  Remember to start your script with a shebang !

Exercise 2:

Modify the shell script from exercise 1 to include a variable.  The variable will hold the contents of the message "Shell Scripting is Fun!".

Exercise 3:

Store the output of the command "hostname" in a variable.  Display "This script is running on _______." where "_______" is the output of the "hostname" command.

Hint:  It's a best practice to use the ${VARIABLE} syntax if there is text or characters that directly precede or follow the variable.

Exercise 4:

Write a shell script to check to see if the file "/etc/shadow" exists.  If it does exist, display "Shadow passwords are enabled."  Next, check to see if you can write to the file.  If you can, display "You have permissions to edit /etc/shadow."  If you cannot, display "You do NOT have permissions to edit /etc/shadow."

Exercise 5:

Write a shell script that displays "man", "bear", "pig", "dog", "cat", and "sheep" on the screen with each appearing on[…]”

Excerpt From: Cannon, Jason. “Shell Scripting: How to Automate Command Line Tasks Using Bash Scripting and Shell Programming”. Apple Books. 

“Solutions to the Practice Exercises

Exercise 1:

#!/bin/bash

echo "Shell Scripting is Fun!"

Exercise 2:

#!/bin/bash

MESSAGE="Shell Scripting is Fun!"

echo "$MESSAGE"

Exercise 3:

#!/bin/bash

HOST_NAME=$(hostname)

echo "This script is running on ${HOST_NAME}."

Exercise 4:

#!/bin/bash

FILE="/etc/shadow"

if [ -e "$FILE" ]

then

  echo "Shadow passwords are enabled."

fi

if [ -w "$FILE" ]

then

  echo "You have permissions to edit ${FILE}."

else

  echo "You do NOT have permissions to edit ${FILE}."

fi

Exercise 5:

#!/bin/bash

for ANIMAL in man bear pig dog cat sheep

do

“ echo "$ANIMAL"

done

Exercise 6:

#!/bin/bash

read -p "Enter the path to a file or a directory: " FILE

if [ -f "$FILE" ]

then

  echo "$FILE is a regular file."

elif [ -d "$FILE" ]

then

  echo "$FILE is a directory."

else

  echo "$FILE is something other than a regular file or directory."

fi

ls -l $FILE

Exercise 7:

#!/bin/bash

FILE=$1

if [ -f "$FILE" ]

then

  echo "$FILE is a regular file."

elif [ -d "$FILE" ]

then

  echo "$FILE is a directory."

else

  echo "$FILE is something other than a regular file or directory."

fi

ls -l $FILE

Exercise 8:

#!/bin/bash

for FILE in $@

do

  if [ -f "$FILE" ]

  then

    echo "$FILE is a regular file."

  elif [ -d "$FILE" ]

  then

    echo "$FILE is a directory."

  else

    echo "$FILE is something other than a regular file or directory."

  fi

  ls -l $FILE

done”

Excerpt From: Cannon, Jason. “Shell Scripting: How to Automate Command Line Tasks Using Bash Scripting and Shell Programming”. Apple Books. 

Why you should do shell scripting and what is The Shebang: ?

Why you should do shell scripting :

Whether you have you perform the same task, again and again, every day and it is boring, right?  “For example, if there is a slight chance that you will have to perform the same set of commands again, to make it easier you should try to create a shell script then and there you have to do it again.  
When I need to do that task again, I could execute that script.  If maintenance needs to be performed on a system at 3:00 in the morning, we can write a script that does the required work and schedule a job to run it.”

SHELL SCRIPTING, in brief:- 

• A script is a command-line program that contains a series of commands. 
• The commands contained in the script are executed by an interpreter. 
• In the case of shell scripts, the shell acts as the interpreter and executes the commands listed in the script one after the other.
• Anything you can execute at the command line, you can put into a shell script.  
• Shell scripts are great at automating tasks.  
• If you find yourself running a series of commands to accomplish a given task and will need to perform that task again in the future, you can—and probably should—create a shell script for that task.

A simple shell script:-

The name of this script is the script.sh  

#!/bin/bash

echo "Hello, this is my first script and it's awesome!"

Before you try to execute the script, make sure that it is executable

$ chmod 755 script1.sh

$ chmod  +x script1.sh

Here is what happens when you execute the script.

$ ./script.sh

The Shebang:

You'll notice that the first line of the script starts with #! followed by the path to the bash shell program, /bin/bash. 

The number sign is very similar to the sharp sign used in music notations - “Also, some people refer to the exclamation mark as a "bang."  So, #! can be spoken as "sharp bang."  The term "Shebang" is an inexact contraction of "sharp bang."

When a script's first line starts with a shebang, what follows is used as the interpreter for the commands listed in the script.  Here are three examples of shell scripts, each using a different shell program as the interpreter.”

- Excerpt From Cannon, Jason. “Shell Scripting: How to Automate Command Line Tasks Using Bash Scripting and Shell Programming”. Apple Books.  

Launch GCP instance for the first time

 

  Launch GCP instance for the first time