# Day 5: Advanced Linux Shell Scripting & User Management for DevOps Engineers

---

### **Task 1: Create Directories Using Shell Script:**

\- Write a bash script [`createDirectories.sh`](http://createdirectories.sh/) that, when executed with three arguments (directory name, start number of directories, and end number of directories), creates a specified number of directories with a dynamic directory name.

```bash
#!/bin/bash

# Check for the correct number of arguments
if [[ $# -ne 3 ]]; then
  echo "Usage: $0 <directory_name> <start_number> <end_number>"
  exit 1
fi

# Get script arguments
dir_name="$1"
start_num="$2"
end_num="$3"

# Loop through numbers and create directories
for (( i=$start_num; i<=$end_num; i++ )); do
  # Create directory with dynamic name
  mkdir "$dir_name$i"
  if [[ $? -ne 0 ]]; then
    echo "Error creating directory: $dir_name$i"
  fi
done

echo "Created directories from $dir_name$start_num to $dir_name$end_num"
```

**Explanation:**

1. **Shebang (#!):** The first line `#!/bin/bash` specifies the interpreter for the script, which is bash in this case.
    
2. **Argument Check:**
    
    * `if [[ $# -ne 3 ]]`: This checks if the number of arguments passed to the script is not equal to 3 (`$#` represents the number of arguments).
        
    * `echo "Usage..."`: If not 3 arguments, it displays the correct usage message.
        
    * `exit 1`: Exits the script with an error code (1).
        
3. **Get Arguments:**
    
    * `dir_name="$1"`: Stores the first argument (directory name) in `dir_name`.
        
    * `start_num="$2"`: Stores the second argument (start number) in `start_num`.
        
    * `end_num="$3"`: Stores the third argument (end number) in `end_num`.
        
4. **Loop and Create Directories:**
    
    * `for (( i=$start_num; i<=$end_num; i++ ))`: This for loop iterates from `start_num` to `end_num` with increment of 1 in variable `i`.
        
    * `mkdir "$dir_name$i"`: Inside the loop, it creates a directory with the name formed by concatenating `dir_name` and the current value of `i`.
        
    * `if [[ $? -ne 0 ]]`: This checks if the `mkdir` command returned an error (non-zero exit code).
        
        * `echo "Error creating directory: $dir_name$i"`: If an error occurs, it displays an error message with the specific directory name.
            
5. **Success Message:**
    
    * After the loop completes, it prints a success message indicating the range of created directories.
        

---

### **Task 2: Create a Script to Back Up All Your Work:**

```bash
#!/bin/bash

# Set your project directory and backup destination

SOURCE_DIR="$HOME/my_project"  # Change this to your project directory
BACKUP_DIR="$HOME/backups"
TIMESTAMP=$(date +"%Y%m%d_%H%M%S")
BACKUP_FILE="${BACKUP_DIR}/backup_${TIMESTAMP}.tar.gz"

# Create the backup directory if it doesn’t exist

mkdir -p $BACKUP_DIR

# Compress and back up the source directory

tar -czf $BACKUP_FILE $SOURCE_DIR

# Check if the backup was successful

if [ $? -eq 0 ]; then
    echo "Backup successful! File stored at: $BACKUP_FILE"
else
    echo "Backup failed!"
fi
```

#### **How it Works:**

* It **compresses** your project folder and creates a **backup** in the `backups` folder.
    
* The backup filename includes a **timestamp** for easy tracking (e.g., `backup_20231011_143000.tar.gz`).
    
* If the backup succeeds, you’ll see a success message. ✅
    

You can now run this script manually whenever you need a backup!

---

### **Task 3: Automate the Backup with Cron ⏰**

Let’s automate the backup process using **cron**—a Linux tool for scheduling tasks. Instead of running the backup script manually, we’ll schedule it to run automatically every day at midnight. 🌙

#### **Steps:**

1. Open the cron job editor:
    

```bash
crontab -e
```

2. Add this line to schedule the backup:
    
    ```bash
     0 0 * /path/to/backup.sh
    ```
    
    This tells the system to run [`backup.sh`](http://backup.sh/) [**every day**](http://backup.sh/) at 12:00 AM.
    

---

### **Task 4: Create Two Users**

Linux allows you to manage users on your system easily. Let’s create two new users using the `useradd` command.

#### **Steps:**

1. **Create two users:**
    
    ```bash
     sudo useradd -m user1
     sudo useradd -m user2
    ```
    
2. **Set passwords for the users:**
    
    ```bash
     sudo passwd user1
     sudo passwd user2
    ```
    
3. **Display the usernames:**
    
    ```bash
     awk -F':' '{ print $1 }' /etc/passwd | tail -n 2
    ```
    

The above command will show the last two users created on the system, which are `user1` and `user2`.