Shell Scripting

For Loop

#!/bin/bash
for i in {1..5}
do
    echo "Hello $i"
done

4 Digits Loop

#!/bin/bash
for i in {0000..9999}
do
    echo $i
done

Read Text Line by Line

read-text.sh

#!/bin/bash
while read line
do
    echo $line
done < example.txt

Retrieve Arguments

Getopts is useful. Create "my_opt.sh".

#!/bin/bash

getopts c cmd
echo $cmd

Run. This output is the current username.

./my_opt.sh -cwhoami

• While Loop and Retrieving Arguments

  Create “my_while_opt.sh”.
  
  ```sh
  while getopts ab: flag
  do
      case "${flag}" in
          a) command1=${OPTARG};;
          b) command2=${OPTARG};;
      esac
  done
  
  cmd1=$($command1)
  echo $cmd1
  cmd2=$($command2)
  echo $cmd2

  Run. This output is the current username and current time.

  ./my_while_opt.sh -awhoami -btime
  # kali
  # real  1111.11s ...