Introduction

Ever wondered how to handle command-line arguments like a pro in your Bash scripts? Here are some nifty techniques to make your scripts more versatile:

💡 Positional Parameters:

Access arguments directly using $1, $2, …, $n. Simple and straightforward!

#!/usr/bin/env bash
echo "First argument: $1"
echo "Second argument: $2"

🌀 Special Variables ($@, $*):

$@ represents all parameters as separate words, while $* combines them into one. Flexibility at its best!

#!/usr/bin/env bash
for arg in "$@"; do
    echo "$arg"
done

🔀 Using shift to Shift Arguments:

Shift positional parameters to the left, discarding the first one. Great for iterative processing!

#!/usr/bin/env bash
while [ "$#" -gt 0 ]; do
    echo "Argument: $1"
    shift
done

🔍 getopts for Option Parsing:

Perfect for handling options and their arguments with finesse!

#!/usr/bin/env bash
while getopts ":a:b:" opt; do
    case $opt in
        a) arg_a="$OPTARG";;
        b) arg_b="$OPTARG";;
        \?) echo "Invalid option: -$OPTARG" >&2; exit 1;;
    esac
done
echo "Option a: $arg_a"
echo "Option b: $arg_b"

🔄 Using shift with getopts:

Combine shift and getopts for advanced option handling and processing of remaining arguments.

#!/usr/bin/env bash
while getopts ":a:b:" opt; do
    case $opt in
        a) arg_a="$OPTARG";;
        b) arg_b="$OPTARG";;
        \?) echo "Invalid option: -$OPTARG" >&2; exit 1;;
    esac
done
shift $((OPTIND-1))
echo "Option a: $arg_a"
echo "Option b: $arg_b"
echo "Remaining arguments: $@"

📝 Read from Command Line:

Use the read command to read input directly from the command line. Simple user interaction!

#!/usr/bin/env bash
echo -n "Enter your name: "
read name
echo "Hello, $name!"

🚀 Example:

Here’s a production-ready and clean script to calculate square of a number.

📝 Script: Calculate Square

#!/usr/bin/env bash

############################################################
# Help Function: Display information about the script
############################################################
Help() {
   echo "Usage: $0 -n <number>"
   echo "Calculate the square of a number."
   echo
   echo "Options:"
   echo "-n    Specify the number for which to calculate the square."
   echo "-h    Display this help message."
   echo
   exit
}

############################################################
# Main Program Section: Placeholder for script logic
############################################################

# Set default value
Number=""

############################################################
# Process the input options. Add options as needed.
############################################################
while getopts ":hn:" option; do
   case $option in
      h) # display Help
         Help;;
      n) # Specify a number
         Number=$OPTARG;;
     \?) # Invalid option
         echo "Error: Invalid option"
         exit 1;;
   esac
done

############################################################
# Validate and perform the task
############################################################

# Check if the number is provided
if [ -z "$Number" ]; then
   echo "Error: Please provide a number using the -n option."
   exit 1
fi

# Check if the provided input is a valid number
if ! [[ "$Number" =~ ^[0-9]+$ ]]; then
   echo "Error: '$Number' is not a valid number."
   exit 1
fi

# Calculate the square
Square=$((Number * Number))

# Display the result
echo "The square of $Number is: $Square"

# Additional script logic goes here...

💡 How to Use:

  • Run the script with -n to specify the number for calculating the square.
  • Use -h to display the help message.
./square_calculator.sh -n 5