Shell Scripting: Mastering Conditions (if, elif, else)

What Are Conditions in Shell?

In Shell scripting, conditions let you:

✅ Check if something is true or false

✅ Make decisions inside your scripts

Instead of running blindly, your script thinks at every step.

🛠️ Basic Syntax

#!/bin/bash

if [ condition ]; then
   commands
elif [ another_condition ]; then
   commands
else
   commands
fi

        

✅ Important:

• [ ] [ ] square brackets with spaces inside
• End your condition block with fi (reverse of if)

📚 Example 1: Simple if

#!/bin/bash

disk_usage=85

if [ "$disk_usage" -gt 80 ]; then
  echo "Warning: Disk usage above 80%!"
fi

        

✅ Checks if disk_usage is greater than 80%.

📚 Example 2: if...else

#!/bin/bash

server_status="down"

if [ "$server_status" = "up" ]; then
  echo "Server is running."
else
  echo "Server is down."
fi

        

✅If condition is true → one block runs.

Else → another block runs.

📚 Example 3: if...elif...else

#!/bin/bash

memory_usage=65

if [ "$memory_usage" -gt 90 ]; then
  echo "Critical: Memory usage very high!"
elif [ "$memory_usage" -gt 70 ]; then
  echo "Warning: Memory usage moderately high."
else
  echo "Memory usage is normal."
fi

        

✅ Multiple layers of conditions = smarter decision trees.

Observability Real-World Example

✅ A script to alert based on CPU Load:

#!/bin/bash

cpu_load=$(uptime | awk -F'load average:' '{ print $2 }' | cut -d',' -f1 | sed 's/ //g')

cpu_load_int=${cpu_load%.*} # Remove decimal part

if [ "$cpu_load_int" -gt 8 ]; then
  echo "Critical Alert: CPU load too high!"
elif [ "$cpu_load_int" -gt 4 ]; then
  echo "Warning: CPU load moderate."
else
  echo "CPU load normal."
fi

        

✅ Smart automation: Different actions depending on CPU load.

🗺️ Where Are We in the Journey?

Linux Fundamentals → Kubernetes Observability → Shell Basics → (Now) Conditions → Loops → Functions

        

✅

You are learning to make your scripts think like engineers.