shell programming functions

 

Functions enable you to break down the overall functionality of a script into smaller, logical subsections, which can then be called upon to perform their individual tasks when needed.

Using functions to perform repetitive tasks is an excellent way to create code reuse. This is an important part of modern object-oriented programming principles.

Shell functions are similar to subroutines, procedures, and functions in other programming languages.

Creating Functions

To declare a function, simply use the following syntax −

function_name () {

   list of commands

}

The name of your function is function_name, and that's what you will use to call it from elsewhere in your scripts. The function name must be followed by parentheses, followed by a list of commands enclosed within braces.

Example

 

# Define your function here

Hello () {

   echo "Hello World"

}

# Invoke your function

Hello

Pass Parameters to a Function

You can define a function that will accept parameters while calling the function. These parameters would be represented by $1, $2 and so on.

Example

# Define your function here

Hello () {

   echo "Hello World $1 $2"

}

# Invoke your function

Hello s3channel

 

Returning Values from Functions

If you execute an exit command from inside a function, its effect is not only to terminate execution of the function but also of the shell program that called the function.

If you instead want to just terminate execution of the function, then there is way to come out of a defined function.

Based on the situation you can return any value from your function using the return command whose syntax is as follows −

return code

Here code can be anything you choose here, but obviously you should choose something that is meaningful or useful in the context of your script as a whole.

Example

Hello () {

   echo "Hello World $1 $2"

   return 10

}

# Invoke your function

Hello Zara Ali

# Capture value returnd by last command

ret=$?

echo "Return value is $ret"