🔧Error Handling in Shell Scripting .

Handling errors is like having a safety net for your shell scripts! 🎯 Today, you’ll learn how to catch mistakes, clean up when things go wrong, and display meaningful messages. Let’s make scripting simple and reliable! 🚀

What You’ll Learn 📚

• Exit Status ($?): Know if a command succeeded or failed.

  • ✅ 0: Success

  • ❌ Non-zero: Failure

• Error Handling with if: Check for errors at every step.

• Cleanup with trap: Automatically clean up temporary files and resources.

• Redirect Errors: Save error messages to files for debugging.

• Custom Messages: Provide user-friendly error explanations.

Code Examples and Explanation 🛠️

Task 1 : Checking Exit Status 🔍

#!/bin/bash
mkdir /tmp/mydir
if [ $? -ne 0 ]; then
  echo "❌ Error: Failed to create directory /tmp/mydir."
else
  echo "✅ Success: Directory /tmp/mydir created."
fi

Detailed Explanation:

1. mkdir /tmp/mydir: Attempts to create a directory.

2. $?: Captures the exit status of the last command:

   • 0: Success.

   • Non-zero: Failure.

3. if [ $? -ne 0 ]: Checks if the exit status is not equal to 0 (failure).

4. echo: Prints a success or error message.

Task 2 : Using if for Multiple Steps 🚦

#!/bin/bash
mkdir /tmp/mydir
if [ $? -ne 0 ]; then
  echo "❌ Error: Could not create directory /tmp/mydir."
  exit 1
fi

touch /tmp/mydir/myfile.txt
if [ $? -ne 0 ]; then
  echo "❌ Error: Failed to create file myfile.txt in /tmp/mydir."
else
  echo "✅ Success: File myfile.txt created."
fi

Detailed Explanation:

1. mkdir /tmp/mydir: Creates a directory.

2. if [ $? -ne 0 ]: Checks if creating the directory failed.

3. exit 1: Exits the script with a non-zero status if an error occurs.

4. touch /tmp/mydir/myfile.txt: Creates a file in the new directory.

5. if [ $? -ne 0 ]: Checks if file creation failed.

6. Error or success messages are printed based on the status.

Task 3 : Using trap for Cleanup 🧹

#!/bin/bash
tempfile=$(mktemp)
trap "rm -f $tempfile; echo '🧹 Temporary file deleted.'" EXIT

echo "Temporary file created: $tempfile"
echo "Some data" > $tempfile

# Simulate an unexpected error
exit 1

Detailed Explanation:

1. tempfile=$(mktemp): Creates a unique temporary file and stores its name in the variable tempfile.

2. trap "rm -f $tempfile; echo '🧹 Temporary file deleted.'" EXIT:

   • Sets up a "trap" to delete the temporary file when the script exits (even if it exits unexpectedly).

3. echo "Some data" > $tempfile: Writes some data to the temporary file.

4. exit 1: Simulates an unexpected error and triggers the trap to delete the file.

Task 4 : Redirecting Errors ➡️

#!/bin/bash
cat non_existent_file.txt 2> error.log
echo "Error messages (if any) have been saved to error.log."

Detailed Explanation:

1. cat non_existent_file.txt: Tries to display the contents of a file that doesn’t exist.

2. 2> error.log: Redirects the error message (2 is for standard error) to a file named error.log.

3. echo: Notifies the user that errors are logged in error.log.

Task 5 : Creating Custom Error Messages ✍️

#!/bin/bash
mkdir /tmp/mydir
if [ $? -ne 0 ]; then
  echo "❌ Error: Could not create /tmp/mydir. 
   Please check your permissions or if the directory already exists."
else
  echo "✅ Directory created successfully!"
fi

Detailed Explanation:

1. Command:
   mkdir /tmp/mydir

   • This attempts to create a directory named mydir in the /tmp folder.

2. Exit Status Check:
   if [ $? -ne 0 ]

   • $? holds the exit status of the previous command (mkdir in this case).

   • If the status is not equal to 0 (-ne 0), the command failed.

3. Error Message:
   echo "❌ Error: Could not create /tmp/mydir. Please check..."

   • If the directory couldn’t be created, it prints an error message suggesting possible reasons (e.g., no permissions or the directory already exists).

4. Success Message:
   echo "✅ Success: Directory /tmp/mydir created."

   • If the directory is successfully created, the script prints a success message.

Without proper error handling, scripts can fail silently, leaving behind messy files and incomplete tasks. With these techniques, you can create scripts that are reliable, maintainable, and user-friendly 💡.