laravel composer install 问题：

php-xml

  Problem 1
    - Installation request for phar-io/manifest 1.0.1 -> satisfiable by phar-io/manifest[1.0.1].
    - phar-io/manifest 1.0.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 2
    - Installation request for phpunit/php-code-coverage 5.2.2 -> satisfiable by phpunit/php-code-coverage[5.2.2].
    - phpunit/php-code-coverage 5.2.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 3
    - Installation request for phpunit/phpunit 6.4.3 -> satisfiable by phpunit/phpunit[6.4.3].
    - phpunit/phpunit 6.4.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 4
    - Installation request for theseer/tokenizer 1.1.0 -> satisfiable by theseer/tokenizer[1.1.0].
    - theseer/tokenizer 1.1.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.

解决：

sudo apt install php-xml

php-zip

Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - laravel/installer v2.0.1 requires ext-zip * -> the requested PHP extension zip is missing from your system.
    - laravel/installer v2.0.0 requires ext-zip * -> the requested PHP extension zip is missing from your system.
    - Installation request for laravel/installer ^2.0 -> satisfiable by laravel/installer[v2.0.0, v2.0.1].

ubuntu 安装

sudo apt install php-zip