Day 5 Task: Advanced Linux Shell Scripting for DevOps Engineers with User Management

1) Create Directories Using Shell Script:

Write a bash script 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.
Example 1: When executed as ./createDirectories.sh day 1 90, it creates 90 directories as day1 day2 day3 ... day90.
Example 2: When executed as ./createDirectories.sh Movie 20 50, it creates 31 directories as Movie20 Movie21 Movie22 ... Movie50.
```
  #!/bin/bash

  for ((i=$2 ; i <=$3 ; i++))
  do
          mkdir /home/ubuntu/shaikh/$1$i
  done
```
$1 — First argument

$2 — Second argument

$3 — Third argument

2) Create a Script to Backup All Your Work:
- Backups are an important part of a DevOps Engineer's day-to-day activities. The video in the references will help you understand how a DevOps Engineer takes backups (it can feel a bit difficult but keep trying, nothing is impossible).
```
  #!/bin/bash

  # What you want to back here we qare giving folder path
  backup_files="/home/ubuntu/shaikh/*"

  # Where to backup
  dest="/home/ubuntu/backup"

  # Create filename with date
  day=$(date +"%d-%b-%y")
  mkdir $dest/$day
  # Backup the files
  cp -r $backup_files $dest/$day

  # Print message
  echo
  echo "Backup finished"                                          [ Read 19 lines ]
  date
```
  - %d: This represents the day of the month (two digits, zero-padded if necessary), such as 09 for the 9th day.
  - %b: This gives the abbreviated month name (three letters), such as Oct for October.
  - %y: This represents the last two digits of the year, such as 24 for the year 2024.
    
    output : Allfiles folder get copied in /home/ubuntu/shaikh/* with that
    
    09-Oct-24 folder

3) Read About Cron and Crontab to Automate the Backup Script:

Cron is the system's main scheduler for running jobs or tasks unattended. A command called crontab allows the user to submit, edit, or delete entries to cron. A crontab file is a user file that holds the scheduling information.

Cron is a job scheduler utility, In simple terms it executes described commands/script at a particular predefined interval.

crontab is basically a table in which we maintain all the cron jobs that we need to execute in our system.
command to check the crontab list:
```
  crontab -l
```

create a new cron job and when u run this command first time it will ask you to select editor like nano ,vim etc and then select editor as per you choice and add new line in file:

crontab -e

# In this u have to select a editor in starting.

u will see one file just easer all and write this statement according to this particular blog

0 2 * * * /home/ubuntu/shaikh/backup.sh

# 0 is minute
# 2 is for hour
# third * is for day of mounth (1-31)
# fourth * is for month (1-12)
# fifth * if for day of week (0-7)
# /home/ubuntu/shaikh/backup.sh where is your script file

4) Read About User Management:

A user is an entity in a Linux operating system that can manipulate files and perform several other operations. Each user is assigned an ID that is unique within the system. IDs 0 to 999 are assigned to system users, and local user IDs start from 1000 onwards.
Create 2 users and display their usernames.
```
  #!/bin/bash

  # Create users
  useradd faizan1
  useradd shaikh1

  # Display created users
  echo "Created users:"
  cut -d: -f1 /etc/passwd | grep -E 'faizan1|shaikh1'
```
- Shebang: #!/bin/bash indicates that the script should be run using the Bash shell.
- Creating Users:
  - useradd faizan1: This command creates a user with the username faizan1.
  - useradd shaikh1: This command creates a user with the username shaikh1.
- Displaying Created Users:
  - echo "Created users:": This line prints the message to indicate that the following output will be the created users.
  - cut -d: -f1 /etc/passwd:
    - This command reads the /etc/passwd file, which contains user account information.
    - -d: sets the delimiter to : (the character that separates fields in /etc/passwd).
    - -f1 specifies that only the first field (the username) should be output.
  - grep -E 'faizan1|shaikh1':
    - This filters the output of the cut command to show only lines that match either faizan1 or shaikh1.
    - The -E option allows the use of extended regex syntax, enabling the use of the | operator to match multiple patterns.

so here we completed day5 #happylearning