Install Drupal into a custom directory

  How to install Drupal into a custom directory clearly. What to do if you use a certain directory structure on hosting, or just want to adhere to your standard of directories naming?

We will use Composer for the installation process. 
For example, we want to use the directory htdocs. 
By create-project, we will fetch and pre-install a standard Drupal project template with a "relocated document root", in this case with the name web.

composer create-project drupal/recommended-project ./

Now let's change this folder for our one. 
In order for the composer to do this automatically for us, it is necessary to edit the file composer.json.

cat composer.json > composer.bak
cat composer.bak  | sed 's/"web\//"htdocs\//g' > composer.json
rm composer.bak

Let's create the new required directories,  htdocs for our "relocated document root" and tmp for Drupal needs.

mkdir htdocs tmp

Now we must move the contents of the default directory to the newly created one.

mv  web/.??* htdocs
mv  web/* htdocs

Removing an unnecessary directory

rm -r web

In order for the composer to make the necessary changes due to a change of the document directory, we should run install

composer install