Functions in Linux Shell
Create reusable functions to simplify Linux shell scripts.
Linux shell functions allow you to package a set of commands into one code block which can be called any number of times. This makes your shell programs small in length and increases re-usability of code.
Simple Linux Function
There are two ways to define a Linux function. Method 1 is the most preferred one
Method 1
<function-name> () {
commands
}
Method 2
function <function-name> {
commands
}
Let's use Linux functions to print Hello World
#!/bin/bash
#define the function
hello_world () {
echo "hello world"
}
#call the function
hello_world
You must always first define the function before calling it. By simply giving the function name, you are calling/executing the function.
Linux Function With Parameters
You can pass parameters to Linux functions based on positional reference
hello_world This is default text
$1 = This
$2 = is
$3 = default
$4 = text
....
You refer to parameters passed to a function based on position 1,2,3 and so on. Let's look at another Linux function which accepts parameters to process results
#!/bin/bash
#define the function
hello_world () {
echo "Your first name is: $1"
echo "Your last name is: $2"
}
#call the function
hello_world Arun Kumar
Simple Calculator With Linux Functions
Let's use a Linux function to get sum of two numbers
#!/bin/bash
#create function to add
add_num () {
sum=$(( $1+$2 ))
echo "Total: $sum"
}
#ask two numbers from the user
read -p "Enter number 1: " num1
read -p "Enter number 2: " num2
add_num num1 num2
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