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Sometimes we need to create a dynamic function which can be executed in both without passing any arguments or without passing any arguments. For this we need to set some default values ​​for those arguments so that if the arguments are not passed while calling the function, it can use the default arguments.

This article will demonstrate how to create optional input parameters for functions. We will also look at some examples and explanations to make the topic easier to understand.

Getting optional input arguments in Bash

In the following example, we are printing the default values. We have declared 4 variables which contain the default values.

The code for our example is as follows:

VAR1=${1:-foo}
VAR2=${2:-bar}
VAR3=${3:-1}
VAR4=${4:-$(date)}

echo "$VAR1"
echo "$VAR2"
echo "$VAR3"
echo "$VAR4"

After executing the code, we will get the following output:

foo
bar
1
Sat Aug 13 14:59:31 +06 2022

Now let's look at an advanced example. In the example shared below, we have created a function that can take 0, 1, and 2 parameters and set the default value inside the function.

Now, the code for our example looks like this:

FindSum()
{
    VAR1=${1:-40}
    VAR2=${2:-50}

    if [ $# -lt 1 ];
    then
        echo "The provided parameters are: $VAR1, $VAR2."
    elif [ $# -lt 2 ];
    then
        echo
        echo "The provided parameters is: $VAR2."
    else
        echo
        echo "No parameters provided"
        VAR1=$1
        VAR2=$2
    fi
    SUM=$((VAR1+VAR2))
    echo "The sum of $VAR1 and $VAR2 is $SUM"
}

FindSum
FindSum 40
FindSum 70 30

Let's explain the code piece by piece.

First, we set the default values ​​of the variables using the lines VAR1=${1:-40}and VAR2=${2:-50}. Afterwards, we check if values ​​for these variables were given.

If the value does not provide them, we have to use its default value; otherwise, use the value given by the user.

Finally, we have just SUM=$((VAR1+VAR2))performed a sum operation using the row and printed the result. Here, we have called the function with FindSum without any parameters.

Similarly, we call a function with one parameter using FindSum line 40. We call a function with two parameters using FindSum line 70 30.

The provided parameters are: 40, 50.
The sum of 40 and 50 is 90

The provided parameters is: 50.
The sum of 40 and 50 is 90

No parameters provided
The sum of 70 and 30 is 100

All the codes used in this article are written in Bash. It will only work in Linux Shell environment.