Day 11 Mastering🖥️ Error Handling in Shell Scripting🎯

Error handling in shell scripting is essential for building resilient scripts that can handle unexpected situations gracefully

Task 1: Checking Exit Status

Objective: Write a script that tries to create a directory and checks if the command was successful. If it fails, print an error message.

#!/bin/bash

# Task 1: Checking Exit Status

# Attempt to create a directory
mkdir /tmp/mydir

# Check if the command was successful
if [ $? -ne 0 ]; then
  echo "Failed to create directory /tmp/mydir"
else
  echo "Directory /tmp/mydir created successfully"
fi

Task 2: Using If Statements for Error Checking

Objective: Extend the script to include more commands (e.g., creating a file inside the directory). Use if statements to check if each command is successful.

#!/bin/bash

# Task 2: Using if Statements for Error Checking

# Define the directory and file names
dir_name="/tmp/mydir"
file_name="$dir_name/myfile.txt"

# Attempt to create a directory
if mkdir "$dir_name"; then
  echo "Directory $dir_name created successfully."
else
  echo "Failed to create directory $dir_name."
  exit 1
fi

# Attempt to create a file inside the directory
if touch "$file_name"; then
  echo "File $file_name created successfully."
else
  echo "Failed to create file $file_name."
  exit 1
fi

Task 3: Using Trap for Cleanup

Objective: Write a script that creates a temporary file and sets a trap to delete the file if the script exits unexpectedly.

#!/bin/bash

# Task 3: Using trap for Cleanup

# Create a temporary file
tempfile=$(mktemp)

# Set a trap to delete the file if the script exits unexpectedly
trap "rm -f $tempfile" EXIT

# Write to the temporary file
echo "This is a temporary file." > "$tempfile"

# Display the contents of the temporary file
cat "$tempfile"

# Simulate an error (you can comment this line to see the cleanup)
exit 1

Task 4: Redirecting Errors

Objective: Write a script that tries to read a non-existent file and redirects the error message to a file called error.log.

#!/bin/bash

# Task 4: Redirecting Errors

# Attempt to read a non-existent file and redirect error to error.log
cat non_existent_file.txt 2> error.log

# Inform the user
echo "Attempted to read non_existent_file.txt. Check error.log for details."

Task 5: Creating Custom Error Messages

Objective: Modify one of the previous scripts to include custom error messages that provide more context about what went wrong.

#!/bin/bash

# Task 5: Creating Custom Error Messages

# Attempt to create a directory
dir_name="/tmp/mydir"

if mkdir "$dir_name"; then
  echo "Directory $dir_name created successfully."
else
  echo "Error: Directory $dir_name could not be created. Check if you have the necessary permissions."
  exit 1
fi

# Attempt to create a file inside the directory
file_name="$dir_name/myfile.txt"

if touch "$file_name"; then
  echo "File $file_name created successfully."
else
  echo "Error: File $file_name could not be created. Check if the directory exists."
  exit 1
fi

Running the Scripts

1. Save each script to a separate file, for example, task1.sh, task2.sh, etc.

2. Make each script executable:chmod +x task1.sh

3. Run the scripts:./task1.sh

Summary of Error Handling Techniques Used

• Exit Status Checking: After each command, we check the exit status using $?.

• If Statements for Error Checking: Using if statements to check for success or failure of commands and handle errors accordingly.

• Using trap for Cleanup: Setting up a trap command to clean up temporary files when the script exits.

• Redirecting Errors: Redirecting error messages to a file using 2>.

• Creating Custom Error Messages: Providing meaningful error messages to help with debugging.

  By mastering these error-handling techniques, you’ll build a solid foundation for writing reliable, resilient shell scripts. These practices empower you to handle unexpected scenarios gracefully, improve script stability, and create maintainable code ready for production environments.