Shell & Scripting

A program that takes commands from the user and sends them to the OS (e.g., Bash, Zsh)

✅ Key Concepts:

• What is a Shell?

  • A program that takes commands from the user and sends them to the OS (e.g., Bash, Zsh).

• Popular Shell: bash (Bourne Again SHell)

✅ Basic Script Example:

#!/bin/bash
echo "Hello, DevOps!"

✅ How to Run a Script:

chmod +x script.sh      # Make it executable
./script.sh             # Run the script

---

Variables and User Input

✅ Define and Use Variables:

name="DevOpsUser"
echo "Welcome, $name"

✅ Read Input:

echo "Enter your name:"
read username
echo "Hello, $username"

✅ Quoting:

• Double quotes " " allow variable expansion

• Single quotes ' ' treat everything literally

---

Conditional Statements

✅ If-Else Syntax:

if [ "$name" == "admin" ]; then
  echo "Welcome, Admin"
else
  echo "Access Denied"
fi

✅ File Test Examples:

if [ -f /etc/passwd ]; then
  echo "File exists"
fi

---

Loops

✅ For Loop:

for i in 1 2 3; do
  echo "Loop #$i"
done

✅ While Loop:

count=1
while [ $count -le 5 ]; do
  echo "Count: $count"
  ((count++))
done

---

Functions

✅ Define and Call a Function:

say_hello() {
  echo "Hello from a function"
}
say_hello

✅ Return Values:

sum() {
  return $(($1 + $2))
}
sum 3 4
echo $?  # Outputs 7

After learning the basic concept of Bash script. we can do the practice for writing any script which may help us to do our work. Like just an example of Update your system, cleans temp files & checks disk space etc.

#!/bin/bash
echo "Updating Linux based system..."
sudo apt update && sudo apt upgrade -y

echo "Cleaning /tmp..."
rm -rf /tmp/*

echo "Disk usage:"
df -h

save this file as “maintenance.sh” and execute it. it will return output like given below.

$ ./maintenance.sh
Updating system...
Hit:1 http://security.ubuntu.com/ubuntu focal-security InRelease
Hit:2 http://archive.ubuntu.com/ubuntu focal InRelease
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
  openssl libssl1.1 ...
N upgraded, 0 newly installed, 0 to remove and N not upgraded.
Need to get 3,000 kB of archives.
After this operation, 1,024 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
...
Cleaning /tmp...

Disk usage:
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        50G   15G   32G  32% /
tmpfs           1.9G  2.1M  1.9G   1% /tmp

🔥 Next Steps: Once you're comfortable, dive into Git, Bash scripting, Ansible, Docker, and Kubernetes — all of which build on these Linux foundations.

Thanks for reading, Happy Learning ~Prem G

#Linux #Bash #Scripting #DevOps #SysAdmin #CloudComputing #DevOpsJourney #TechLearning #LinuxForDevOps #LearningInPublic #TechJourney #30DaysOfDevOps #shubhamLondhe #TrainWithShubham #KorboLorboJeetbo