How to fix issue for install laravel 5.6?

Question

I upgrade PHP 7.0 to 7.1 in ubuntu 16.04.

I need install laravel 5.6, but show this error:

But after run composer create-project --prefer-dist laravel/laravel blog in terminal show this error:

Installing laravel/laravel (v5.6.0)
- Installing laravel/laravel (v5.6.0): Loading from cache
Created project in orouji6
> @php -r "file_exists('.env') || copy('.env.example', '.env');"
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

Problem 1
   - phpunit/phpunit 7.1.x-dev requires ext-dom * -> the requested PHP extension dom is missing from your system.
   - phpunit/phpunit 7.0.x-dev requires ext-dom * -> the requested PHP extension dom is missing from your system.
   - phpunit/phpunit 7.0.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.
   - phpunit/phpunit 7.0.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.
   - Installation request for phpunit/phpunit ~7.0 -> satisfiable by phpunit/phpunit[7.0.0, 7.0.1, 7.0.x-dev, 7.1.x-dev].

To enable extensions, verify that they are enabled in your .ini files:
- /etc/php/7.1/cli/php.ini
- /etc/php/7.1/cli/conf.d/10-mysqlnd.ini
- /etc/php/7.1/cli/conf.d/10-opcache.ini
- /etc/php/7.1/cli/conf.d/10-pdo.ini
- /etc/php/7.1/cli/conf.d/20-calendar.ini
- /etc/php/7.1/cli/conf.d/20-ctype.ini
- /etc/php/7.1/cli/conf.d/20-exif.ini
- /etc/php/7.1/cli/conf.d/20-fileinfo.ini
- /etc/php/7.1/cli/conf.d/20-ftp.ini
- /etc/php/7.1/cli/conf.d/20-gettext.ini
- /etc/php/7.1/cli/conf.d/20-iconv.ini
- /etc/php/7.1/cli/conf.d/20-json.ini
- /etc/php/7.1/cli/conf.d/20-mbstring.ini
- /etc/php/7.1/cli/conf.d/20-mysqli.ini
- /etc/php/7.1/cli/conf.d/20-pdo_mysql.ini
- /etc/php/7.1/cli/conf.d/20-phar.ini
- /etc/php/7.1/cli/conf.d/20-posix.ini
- /etc/php/7.1/cli/conf.d/20-readline.ini
- /etc/php/7.1/cli/conf.d/20-shmop.ini
- /etc/php/7.1/cli/conf.d/20-sockets.ini
- /etc/php/7.1/cli/conf.d/20-sysvmsg.ini
- /etc/php/7.1/cli/conf.d/20-sysvsem.ini
- /etc/php/7.1/cli/conf.d/20-sysvshm.ini
- /etc/php/7.1/cli/conf.d/20-tokenizer.ini
You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.

How to fix this problem? Thanks

Answer 1

You need to install php dom extension.

sudo apt-get install php7.1-xml