As you progress from basic to intermediate shell scripting, you begin to unlock more powerful capabilities, allowing for more complex automation and system management tasks. This blog will cover essential intermediate concepts such as conditional statements, loops, functions, and script parameters, providing relevant examples to illustrate their use.

1. Conditional Statements: Making Decisions in Scripts

Conditional statements enable your script to make decisions based on certain conditions. The if-elif-else structure is fundamental in shell scripting:

bash
#!/bin/bashecho “Enter a number:”
read number
if [ $number -gt 10 ]; then
 echo “The number is greater than 10.”
elif [ $number -eq 10 ]; then
 echo “The number is exactly 10.”
else
 echo “The number is less than 10.”
fi

In this example, the script reads a number from the user and prints a message based on the value of the number.

2. Loops: Automating Repetitive Tasks

Loops allow you to execute a series of commands repeatedly. The for loop and while loop are commonly used in shell scripting:

For Loop:

bash
#!/bin/bash
for i in {1..5}; do
 echo “Iteration $i”
done

While Loop:

bash
#!/bin/bash
count=1
while [ $count -le 5 ]; do
 echo “Count: $count”
 count=$((count + 1))
done

These loops help automate repetitive tasks, such as processing files or executing commands multiple times.

3. Functions: Organizing Code for Reusability

Functions make scripts more modular and easier to maintain by encapsulating code into reusable blocks. Here’s how to define and use functions:

bash
#!/bin/bash
# Define a function
greet() {
 local name=$1
 echo “Hello, $name!”
}
# Call the function
greet “Alice”
greet “Bob”

In this example, greet is a function that takes one argument (name) and prints a greeting message. Using local ensures the variable scope is limited to the function.

4. Script Parameters: Enhancing Script Flexibility

Scripts can accept parameters to make them more flexible and reusable. Parameters are accessed using $1, $2, etc., where $1 is the first parameter, $2 is the second, and so on:

bash
#!/bin/bash
if [ $# -lt 2 ]; then
 echo “Usage: $0 <name> <age>”
 exit 1
fi
name=$1
age=$2
echo “Name: $name, Age: $age”

This script checks if at least two parameters are provided and then uses them within the script. $# gives the number of parameters passed to the script.

5. Arrays: Handling Multiple Values

Arrays are useful for storing and processing lists of data. Here’s an example of how to declare and use arrays in a shell script:

bash
#!/bin/bash
# Declare an array
fruits=(“Apple” “Banana” “Cherry”)
# Access array elements
echo “First fruit: ${fruits[0]}”
# Loop through the array
for fruit in “${fruits[@]}”; do
 echo “Fruit: $fruit”
done

This script demonstrates how to declare an array, access individual elements, and iterate through all elements.

6. Error Handling: Creating Robust Scripts

Handling errors is crucial for creating reliable scripts. The set -e command makes the script exit immediately if any command fails:

bash
#!/bin/bash
set -e
mkdir /some/directory
cd /some/directory
touch file.txt
echo “All commands executed successfully!”

For more control, you can use trap to catch errors and execute a specific function:

bash
#!/bin/bash
trap ‘echo “An error occurred. Exiting…”; exit 1;’ ERR
echo “Executing command…”
false # This command will fail
echo “This line will not be executed.”

Conclusion

Intermediate shell scripting in Linux opens up new possibilities for automation and system management. By mastering conditional statements, loops, functions, script parameters, arrays, and error handling, you can create more powerful and flexible scripts. These concepts form the foundation for advanced scripting techniques and enable you to tackle more complex tasks efficiently.

Happy scripting!