However, this error appeared when I am trying to create a new Laravel 5 project,
You made a reference to a non-existent script @php -r "file_exists('.env') || copy('.env.example', '.env');"
Loading composer repositories with package information
. . .
You made a reference to a non-existent script @php artisan key:generate
Lets fix this in one step;
Step 1: Update the composer,$ composer self-update
Updating to version 1.5.2 (stable channel).
Use composer self-update --rollback to return to version 1.2.2
Run the command used to create the new project,
$ composer create-project laravel/laravel myapps