Lock files for single instance in Bash Scripting - Mini Project: Build & Apply

Lock files for single instance

📖 Scenario: You want to run a script that should only have one copy running at a time. To do this, you will use a lock file. This lock file will tell the script if another copy is already running, so it won't start twice.

🎯 Goal: Build a bash script that creates a lock file when it starts. If the lock file exists, the script will stop and tell the user another instance is running. If not, it will create the lock file, run the main task, then remove the lock file at the end.

📋 What You'll Learn

Create a variable for the lock file path

Check if the lock file exists

Create the lock file if it does not exist

Remove the lock file after the main task

Print a message if another instance is running

💡 Why This Matters

🌍 Real World

Lock files are used in scripts that should not run multiple times at once, like backups or updates, to avoid conflicts.

💼 Career

Many system administrators and automation engineers use lock files to ensure safe script execution without overlap.

1

Create a lock file variable

Create a variable called lockfile and set it to /tmp/myscript.lock.

Bash Scripting

# Your code here

Need a hint?

Use = to assign the string /tmp/myscript.lock to the variable lockfile.

2

Check if the lock file exists

Add an if statement to check if the file at $lockfile exists using test -e. If it exists, print "Another instance is running." and exit the script with status 1.

Bash Scripting

lockfile="/tmp/myscript.lock"
# Your code here

Need a hint?

Use if test -e "$lockfile"; then to check if the file exists.

3

Create the lock file and simulate main task

Create the lock file by using touch on $lockfile. Then simulate the main task by printing "Script is running..." and sleeping for 2 seconds.

Bash Scripting

lockfile="/tmp/myscript.lock"
if test -e "$lockfile"; then
    echo "Another instance is running."
    exit 1
fi
# Your code here

Need a hint?

Use touch "$lockfile" to create the lock file.

4

Remove the lock file and print completion

Remove the lock file using rm on $lockfile. Then print "Script finished and lock released.".

Bash Scripting

lockfile="/tmp/myscript.lock"
if test -e "$lockfile"; then
    echo "Another instance is running."
    exit 1
fi
touch "$lockfile"
echo "Script is running..."
sleep 2
# Your code here

Need a hint?

Use rm "$lockfile" to remove the lock file.