Practice Exercise: Exploring Bash Looping Constructs

Objectives

Learn about different looping constructs in Bash, including for and while loops.
Practice using loops to automate repetitive tasks in Bash scripts.
Create Bash scripts that incorporate for and while loops for various scenarios.

Scenario

Bash provides powerful looping constructs that allow you to automate tasks by repeating a series of commands. In this exercise, you'll explore different looping constructs, including for and while loops, and practice using them to solve real-world problems in Bash scripting.

Tasks

Task 1: Simple `for` Loop

Create a Bash script named simple_for_loop.sh.
Implement a simple for loop that:
Iterates through the numbers 1 to 5.
Prints each number to the console.

Test your script to ensure the for loop correctly prints the numbers.

#!/bin/bash

# Use a for loop to iterate through the numbers 1 to 5
for number in {1..5}
do
  echo "Number: $number"
done

Task 2: `for` Loop with Array

Create a Bash script named for_loop_with_array.sh.
Declare an array of your favorite fruits.
Implement a for loop that:
Iterates through the elements of the array.
Prints a message for each fruit, such as "I like !".

Test your script to verify that it displays messages for each fruit.

#!/bin/bash

# Declare an array of favorite fruits
fruits=("Apple" "Banana" "Orange" "Strawberry" "Mango")

# Use a for loop to iterate through the array and print messages
for fruit in "${fruits[@]}"
do
  echo "I like $fruit!"
done

Task 3: `while` Loop

Create a Bash script named while_loop.sh.
Implement a while loop that:
Asks the user to guess a secret number between 1 and 10.
Checks if the user's guess matches the secret number.
Provides feedback (e.g., "Too high," "Too low") until the user guesses correctly.
Exits the loop when the correct guess is made.
Include logic to generate a random secret number.
Test your script by playing the number guessing game.
Try implementing the guess.sh script on your own. If you get lost refer to the previous exercise

Task 4: Looping through Files

Create a Bash script named loop_through_files.sh.
Choose a directory with multiple files (e.g., text files).
Implement a for loop that:
Iterates through the files in the directory.

Performs an action on each file, such as counting lines or displaying its contents.

#!/bin/bash

# Specify the directory containing the files
directory="/etc/selinux/"

# Check if the directory exists
if [ ! -d "$directory" ]; then
  echo "Directory not found: $directory"
  exit 1
fi

# Use a for loop to iterate through files in the directory
for file in "$directory"/*; do
  # Check if the item is a file (not a directory)
  if [ -f "$file" ]; then
    echo "File: $file"
    # Display the contents of the file
    cat "$file"
    echo "=========================="
  fi
done

Test your script by running it

[intern@intern-a1t-inf-lnx1 ~]$ ./loop_through_files.sh
File: /etc/openldap/ldap.conf
#
# LDAP Defaults
#

# See ldap.conf(5) for details
# This file should be world readable but not world writable.

#BASE   dc=example,dc=com
#URI    ldap://ldap.example.com ldap://ldap-master.example.com:666

#SIZELIMIT  12
#TIMELIMIT  15
#DEREF      never

# When no CA certificates are specified the Shared System Certificates
# are in use. In order to have these available along with the ones specified
# by TLS_CACERTDIR one has to include them explicitly:
#TLS_CACERT /etc/pki/tls/cert.pem

# System-wide Crypto Policies provide up to date cipher suite which should
# be used unless one needs a finer grinded selection of ciphers. Hence, the
# PROFILE=SYSTEM value represents the default behavior which is in place
# when no explicit setting is used. (see openssl-ciphers(1) for more info)
#TLS_CIPHER_SUITE PROFILE=SYSTEM

# Turning this off breaks GSSAPI used with krb5 when rdns = false
SASL_NOCANON    on

==========================

Task 5: Advanced Looping

Create a Bash script named advanced_looping.sh.
Implement a more complex script that combines both for and while loops.
Use a for loop to iterate through a range of numbers (e.g., 1 to 3).
Inside the for loop, use a while loop to ask the user for input until they provide a valid response.

Handle different user inputs and provide feedback.

#!/bin/bash

# Iterate through a range of numbers using a for loop
for i in {1..3}; do
  echo "Iteration $i"

  valid_input=false

  # Use a while loop to repeatedly ask for user input until valid
  while [ "$valid_input" = false ]; do
    read -p "Enter 'yes' or 'no': " user_input

    # Check if the input is either 'yes' or 'no'
    if [ "$user_input" = "yes" ]; then
      echo "You entered 'yes'."
      valid_input=true
    elif [ "$user_input" = "no" ]; then
      echo "You entered 'no'."
      valid_input=true
    else
      echo "Invalid input. Please enter 'yes' or 'no'."
    fi
  done

  echo "=========================="
done

Test your script with various inputs to ensure it works as expected.

[intern@intern-a1t-inf-lnx1 ~]$ chmod +x advanced_looping.sh
[intern@intern-a1t-inf-lnx1 ~]$ ./advanced_looping.sh
Iteration 1
Enter 'yes' or 'no': yes
You entered 'yes'.
==========================
Iteration 2
Enter 'yes' or 'no': no
You entered 'no'.
==========================
Iteration 3
Enter 'yes' or 'no': yes
You entered 'yes'.
==========================

[intern@intern-a1t-inf-lnx1 ~]$ ./advanced_looping.sh
Iteration 1
Enter 'yes' or 'no': asdf
Invalid input. Please enter 'yes' or 'no'.
Enter 'yes' or 'no': yes
You entered 'yes'.
==========================
Iteration 2
Enter 'yes' or 'no': asdfasfd
Invalid input. Please enter 'yes' or 'no'.
Enter 'yes' or 'no': no
You entered 'no'.
==========================
Iteration 3
Enter 'yes' or 'no': adfsasdfyes
Invalid input. Please enter 'yes' or 'no'.
Enter 'yes' or 'no': yes
You entered 'yes'.
==========================

Conclusion

In this exercise, you've explored different looping constructs in Bash, including for and while loops. You've practiced using loops to automate tasks and solve various problems in Bash scripting. Understanding how to implement looping constructs will enhance your ability to create efficient and versatile Bash scripts.