Linux Shell Scripting for DevOps

Shell Types:

• Bash (Bourne Again SHell): Most widely used shell on Linux systems.

• Sh (Bourne Shell): Basic shell available on most Unix systems.

• Zsh (Z Shell): An extended version of Bash with additional features.

• Fish: A user-friendly shell with syntax highlighting and autosuggestions.

Basic Shell Script Structure:

1. Shebang: The first line of the script, specifies the shell interpreter to be used. For Bash, it is #!/bin/bash.

2. Comments: Lines starting with # are comments and are ignored by the shell.

3. Commands: Actual commands to be executed.

#!/bin/bash

# This is a comment
echo "Hello, World!"  # Print Hello, World!

Running a Shell Script:

1. Make the script executable: Run chmod +x script_name.sh to make your script executable.

2. Execute the script: Run ./script_name.sh to execute the script.

Shell Script to install any package into the machine:

#!/bin/bash

echo "installing $1"
sudo apt update -y
sudo apt-get install $1 -y

Variables:

#!/bin/bash

name= "Robin"
echo "My name is $name, Welcome to my blog!"

Output:

Input User:

#!/bin/bash

echo "What is the name of your folder?"
read foldername
mkdir $foldername
echo "folder created, please check..."

Output:

Arguments:

#!/bin/bash

echo "first argument $1"
echo "second argument $2"
echo "all arguments are $1 $2"

Output:

Backup Shell Script:

#!/bin/bash

src_dir=/home/ubuntu/scripts
tgt_dir=/home/ubuntu/backups
current_timestamp=$(date "+%Y-%m-%d-%H-%M-%S")
echo "Taking Backup for Timestamp:" $current_timestamp
final_file=$tgt_dir/scripts-backup-$current_timestamp.tgz
tar czf $final_file -C $src_dir .
echo "Backup Completed..."

Output:

Backup Shell Script (with function):

#!/bin/bash

function create_backup {
         src_dir=/home/ubuntu/scripts
         tgt_dir=/home/ubuntu/backups

         current_timestamp=$(date "+%Y-%m-%d-%H-%M-%S")
         final_file=$tgt_dir/scripts-backup-$current_timestamp.tgz
         tar czf $final_file -C $src_dir .
}
echo "Starting Backup Process..."
create_backup
echo "Backup Completed..."

Output:

Automate Backup Shell Script using Crontab:

To schedule a script to run daily at a specific time using cron jobs, open your terminal or command prompt and type crontab -e to edit the crontab file. Add the following line at the end of the crontab file, replacing /path/to/backup_script.sh with the actual path to your script:

The numbers and asterisks represent the following schedule:

• 0 - Minutes (0 to 59)

• 2 - Hour (0 to 23, where 0 is midnight and 23 is 11 PM)

• * - Wildcard, meaning every day of the month

• * - Wildcard, meaning every month

• * - Wildcard, meaning every day of the week

Happy learning (^_^)