Positional arguments in shell scripts

• The arguments which are passed to the shell script after the filepath of shell becomes positional arguments

./myscript.sh 12 13

• The above example consider

$0 = ./myscript.sh
$1 = 12
$2 = 13

• Lets develop a shell script which takes name and location as positional argument 1 and 2 and prints the message

#!/bin/bash

#####################################################################
# Author: Shaik Khaja Ibrahim
# Version: v1.0.0
# Date: 26-Aug-2020
# Description: This script demonstrates positional arguments
# Usage: ./positionalargdemo.sh <name> <location>
# 1 positional argument is considered as name
# 2 positional argument is considered as location
#####################################################################

name=$1
location=$2

echo "Welcome ${name}, You come from ${location}. Welcome to Bash Scripting"

• Execution Result

Parameters & arguments

• Lets understand the terminology of parameter & arguments. They are slightly different
• Argument is something which you pass to a script.
• What you define in a script to hold argument value is parameter
• Lets write a simple script to demonstrate the difference

#!/bin/bash

#####################################################################
# Author: Shaik Khaja Ibrahim
# Version: v1.0.0
# Date: 25-Aug-2020
# Description: This is shell script demonstrating parameters and arguments
# Usage: ./argumentparameter.sh <arg-1> <arg-2>
#####################################################################

# parameter is used to define argument value
parameter_1=$1

parameter_2=$2

echo "Parameter 1 is ${parameter_1}"

echo "Parameter 2 is ${parameter_2}"

• The scripts which we have developed so far are non-interactive scripts, because once you pass the values the execution happens
• Interactive scripts take inputs from users while executing
• Now lets look at a simple read command which reads the input from the user and stores in a variable called as REPLY
• Now lets execute one more simple variation of the read command
• Lets build some interactive script asking questions to the user

#!/bin/bash

#####################################################################
# Author: Shaik Khaja Ibrahim
# Version: v1.0.0
# Date: 26-Aug-2020
# Description: This is shell script demonstrating interactive scripts
# Usage: ./interactivescriptdemo.sh
#####################################################################

read -p "Name a superhero which you like? " super_hero
read -p "Which movie has this role? " movie_super_hero
read -p "What is your name? " name
echo "Hi ${name}, Thanks for watching movie ${movie_super_hero} and liking the character ${super_hero}"

• Now lets execute the script

• Lets try to come up with script design which acts as a calculator by taking two values and operation as input?

  • Script will be calculator.sh
  • operations that will be supported are add,sub,mul,div
  • It should take two numbers to perform math.