PHP missing extension ext-mbstring during Composer Install or update

When you do

composer install

or

composer update

, you may get following error 

phpunit/phpunit 7.5.9 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.

Your PHP version missing php-mbstring extension, so please go head and install php-mbstring extension using following command.

sudo apt install php-mbstring

For PHP 7.0

sudo apt install php7.0-mbstring

For PHP 7.1

sudo apt install php7.1-mbstring

For PHP 7.2

sudo apt install php7.2-mbstring

For PHP 7.3

sudo apt install php7.3-mbstring

For PHP 7.4

sudo apt install php7.4-mbstring