# Real-Time Shell Scripting – Part 1-Automate Log File Backups Using Shell Script + Cron + GitHub This is the first script in my “10 Real-Time Shell Scripts” collection — where I document useful shell automation tasks with code, explanations, and troubleshooting. In this post, I’ll cover: ✅ Writing a shell script to back up log files  ✅ Automating it using `cron`  ✅ Pushing the script to GitHub from a Linux VM  ✅ Fixing real issues I faced --- ### 1\. The Backup Script (Full Code) Here’s the complete script that backs up `/var/log` files into a timestamped.`tar.gz` archive: `#!/bin/bash` `# Source directory to back up` `source_dir="/var/log"` `# Destination directory` `backup_dir="/home/ubuntu/log_backups"` `# Backup filename with timestamp` `backup_filename="Log_Backup_$(date +'%Y-%m-%d_%H-%M-%S').tar.gz"` `# Create the destination directory if it doesn't exist mkdir -p "$backup_dir"` `# Compress and archive the logs` `tar -czvf "$backup_dir/$backup_filename" "$source_dir"` `# Check if backup was successful` `if [ $? -eq 0 ]; then` `echo "Backup successful: $backup_filename"` `else` `echo "Backup failed" fi` ### OUTPUT: Make sure you give execute permission before you run the code: `sudo chmod +x backup.sh`→ giving execute permissions `./backup.sh`→ running the script ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1751205319225/0aca6b47-252e-4a57-99c3-f211648af6d4.jpeg align="center") ### Line-by-Line Explanation: #### `#!/bin/bash` * **Shebang line**. * Tells the system to execute this script using the **Bash shell** located at `/bin/bash`. --- #### `source_dir="/var/log"` * Creates a variable named `source_dir`. * It stores the **path of the directory** you want to back up. * `/var/log` is typically where system logs are stored in Linux. --- #### `backup_dir="/home/ubuntu/log_backups"` * Defines where you want to save the backup file. * This is the **destination directory** on your system. * `mkdir -p` later ensures this directory exists (or is created). --- #### `backup_filename="Log_Backup_$(date +'%Y-%m-%d_%H-%M-%S').tar.gz"` * Creates a **dynamic filename** for your backup. * `$(date +'%Y-%m-%d_%H-%M-%S')` generates a current timestamp. * Full result: a name like `Log_Backup_2025-06-22_21-30-00.tar.gz` * The `.tar.gz` extension means it will be a **compressed archive**. --- #### `mkdir -p "$backup_dir"` * Makes sure the destination directory exists. * `-p` ensures no error if it already exists and creates **any missing parent directories**. --- #### `tar -czvf "$backup_dir/$backup_filename" "$source_dir"` * This is the **main backup command**. * `tar` is used to archive files. * Flags: * `-c`: create a new archive * `-z`: compress using gzip * `-v`: verbose (shows progress) * `-f`: file name to write to (output archive) * It compresses the source directory into the filename path created above. --- #### `if [ $? -eq 0 ]; then` * `$?` stores the **exit status** of the last executed command. * If `tar` was successful, it will be `0`. * This line starts a conditional check: *Did the backup succeed?* --- #### `echo "Backup successful: $backup_filename"` * This prints a success message with the actual backup filename. --- #### `else` * If `$?` is **not 0**, the backup failed. --- #### `echo "Backup failed"` * This message will print if the backup didn’t complete successfully. --- #### `fi` * Closes the `if` block. --- ## 3\. 🕒 Automate Your Backup Using `cron` You can schedule your backup script to run automatically every day at 2 AM using a cron job. Steps: 1\. Open crontab: `crontab -e` Then enter 1 to open nano editor. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1751205431939/726bb298-9131-4d09-862a-1360a4972a53.jpeg align="center") 2\. Add this line at the bottom: 0 2 \* \* \* /home/ubuntu/backup-script/[backup.sh](http://backup.sh) >> /home/ubuntu/backup-cron.log 2>&1 --- ## 4\. 🐧 Push Your Backup Script to GitHub from Linux VM If you’re using a fresh Linux VM, first make sure Git is installed: Install Git: `sudo apt update sudo apt install git -y` ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1751205535761/8701f7b5-94ec-4818-8f80-c0716449a8dd.jpeg align="center") Clone Your GitHub Repository: `git clone` [`https://github.com/JU2512/10-Real_Time-Shell-Scripts.git` `cd`](https://github.com/JU2512/10-Real_Time-Shell-Scripts.git%EF%BF%BCcd) `10-Real_Time-Shell-Scripts` `mkdir backup-script cd backup-script vi` [`backup.sh`](http://backup.sh) Push Changes to GitHub: > ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1751205612815/0478a9e4-c55e-426d-bb26-3ad597f6ef63.jpeg align="center") `cd ~/10-Real_Time-Shell-Scripts git add . git commit -m "Add log file backup script" git push origin main` --- ## 5\. 🛠️ Troubleshooting: Real Errors I Faced & How I Solved Them ### ❌ 1. "Bad Interpreter: No such file or directory" Problem: Got error `/bin/bash^M: bad interpreter: No such file or directory` when running `./`[`backup.sh`](http://backup.sh) ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1751205861669/0dba770c-d49f-4c3c-bc96-b4936b7d1d9d.jpeg align="center") Solution: I deleted the original file and rewrote it inside the VM using `vi`, which ensured proper Unix line endings. ### ❌ 2. "Permission Denied" When accessing `/var/log` Problem: Script failed with permission error while accessing `/var/log` Solution: Used `sudo ./`[`backup.sh`](http://backup.sh) to run the script with elevated permissions. ### ❌ 3. Unable to Push Code to GitHub Problem: Git push failed due to authentication error ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1751205904523/010fd75f-a81f-4b36-ab11-30232e062f40.jpeg align="center") Solution: \- Generated a new personal access token (PAT) from GitHub with `repo` access \- Used the token when prompted for password during `git push` --- ## 🔜 More Scripts Coming up- Stay tuned Thanks for reading — I hope these examples help you in real-world DevOps work! ***You can get access to more such scripts in my GitHub repo. 🚀*** link → [10\_Real-Time-Scripts](https://github.com/JU2512/10-Real_Time-Shell-Scripts) **Happy Learning:}** 👩‍💻 Jyothi Urade | #FromCloudToOps