Error logging patterns in Bash Scripting - Mini Project: Build & Apply

Error Logging Patterns in Bash Scripts

📖 Scenario: You are writing a simple bash script to run commands and log any errors that happen during execution. Proper error logging helps you find and fix problems quickly.

🎯 Goal: Build a bash script that runs a command, captures errors, and writes error messages to a log file with timestamps.

📋 What You'll Learn

Create a variable to hold the log file path

Create a function to log errors with timestamps

Run a command and capture any error output

Use the error logging function to write errors to the log file

Print a message indicating if the command succeeded or failed

💡 Why This Matters

🌍 Real World

Error logging is essential in scripts that automate tasks, so you can quickly find and fix problems without manually checking outputs.

💼 Career

DevOps engineers and system administrators use error logging patterns to maintain reliable automation scripts and troubleshoot issues efficiently.

1

Create a log file variable

Create a variable called LOG_FILE and set it to "error.log" to store the error log filename.

Bash Scripting

# Create a variable called LOG_FILE and set it to "error.log"
# Your code here

Need a hint?

Use = to assign the string "error.log" to the variable LOG_FILE.

2

Create an error logging function

Create a function called log_error that takes one argument message. Inside the function, append the current date and time followed by the message to the file stored in LOG_FILE. Use date +"%Y-%m-%d %H:%M:%S" to get the timestamp.

Bash Scripting

LOG_FILE="error.log"
# Create a function log_error that appends timestamp and message to LOG_FILE
# Your code here

Need a hint?

Define the function with log_error() { ... }. Use echo with date and append to $LOG_FILE using >>.

3

Run a command and capture errors

Run the command ls /nonexistent_directory and redirect its error output to a variable called error_output. Use command substitution with $( ... ) and redirect standard error with 2>&1.

Bash Scripting

LOG_FILE="error.log"

log_error() {
    echo "$(date +"%Y-%m-%d %H:%M:%S") ERROR: $1" >> "$LOG_FILE"
}

# Run ls /nonexistent_directory and capture error output in error_output
# Your code here

Need a hint?

Use $(ls /nonexistent_directory 2>&1) to capture error output into error_output.

4

Log errors and print result

Check if error_output is not empty. If it has content, call log_error with error_output as argument and print "Command failed, error logged.". Otherwise, print "Command succeeded.".

Bash Scripting

LOG_FILE="error.log"

log_error() {
    echo "$(date +"%Y-%m-%d %H:%M:%S") ERROR: $1" >> "$LOG_FILE"
}

error_output=$(ls /nonexistent_directory 2>&1)

# Check if error_output is not empty, log error, and print message
# Your code here

Need a hint?

Use if [ -n "$error_output" ] to check if the variable is not empty.