Function And Argument In Shell Script

What is Function?

-> If we have to perform repetitive tasks then instead of writing that task every time we write it in a block and whenever needed we run that block and our task gets executed. This block is called a function.

Example - Suppose we have to print "Hello World" 5 times then there is a way to print like -

#!/bin/bash
echo "Hello World"
echo "Hello World"
echo "Hello World"
echo "Hello World"
echo "Hello World"

-> Using this way our task of printing "Hello World" 5 times get completed but suppose we have to print this 1000 times then this will be very time-consuming to do.

-> So instead of writing every time we write our code or task in a block and after that we can call whenever we need.

#!/bin/bash

# There are two ways of definining functions

# 1st Way

function myFunc_1Way {
  echo "Hello, Welcome to 1st Way to define Function In Shell Script"
}

# To call the function, Just write the Function Name and Suppose we have to print above line 3 times then instead of writing that code 3 times, we call the function 3 times as -
myFunc_1Way
myFunc_1Way
myFunc_1Way


# 2nd Way

myFunc_2Way() {
   echo "Hello, Welcome to 2nd Way to define Function In Shell Script"
}

# To call the function
myFunc_2Way

Output -

Passing Arguments in the Function

-> Suppose we want to take the arguments like taking the values from the user or from the variable then we can do as -

#!/bin/bash

# Variables

name="Bhaskar"
age=23

# Defining function

# We can use this variable values in different ways

echo "1st way of using variable value"
echo "-------------------------------"
myInfo() {
echo "My name is $name"
echo "My age is $age"
}

# Calling the Function
myInfo

echo

echo "2nd way of using variable values"
echo "--------------------------------"
myInfo() {
echo "My name is $1"
echo "My age is $2"
}

# Calling the Function
myInfo $name $age

Output -

-> We can take values fro the users also as -

#!/bin/bash

# Taking values from user

read -p "Enter your name : " name
read -p "Enter your age : " age

# Defining function

# We can use this variable values in different ways

echo "1st way of using variable value"
echo "-------------------------------"
myInfo() {
echo "My name is $name"
echo "My age is $age"
}

# Calling the Function
myInfo

echo

echo "2nd way of using variable values"
echo "--------------------------------"
myInfo() {
echo "My name is $1"
echo "My age is $2"
}

# Calling the Function
myInfo $name $age

Output -

Passing Argument While Running Shell Script

-> We can pass the argument when we run the shell script

Ex - bash runtime_args_func.sh <first argument> <second argument> ...

#!/bin/bash

echo "First argument is - $1"

echo "Second argument is - $2"

-> Suppose we run this as - bash runtime_args_func.sh Bhaskar Mehta

-> Here the first argument is Bhaskar and the second argument is Mehta

Output -

-> We can also get how many total arguments have been passed and a list of all the arguments as-

-> To get the total number of arguments use - $# and To get the list of all arguments use - $@

#!/bin/bash

echo "First argument is - $1"

echo "Second argument is - $2"

# To get the total arguments
echo
echo "Total arguments are - $#"

# To get list of all arguments
echo
echo "List of argumnets are - $@"

Output -

-> We can apply for loop on the arguments -

#!/bin/bash

echo "First argument is - $1"

echo "Second argument is - $2"

# To get the total arguments
echo
echo "Total arguments are - $#"

# To get list of all arguments
echo
echo "List of argumnets are - $@"

# Fro loop on the tatal list of arguments -
for args in $@
do
        echo "Argument is $args"
done

Output -

-> When we pass multiple arguments then based on the requirement we can shift the arguments.

-> Suppose we have passed three arguments A B and C and suppose our task is done with argument A and now we want to combine the argument B and C then we can Shift the Argument.

Ex -

#!/bin/bash

echo "First argument is - $1"

# If we want to combine the remaing Argument then we can use shift
shift # Here we are saying that 1st argument is gone, now treat remaing arguments as a single arguments
echo "Second argument is - $@"

Output -