Please follow the Requirements to install required packages in the specific operating system.

To make composer running perfectly, it should ensure that the system-wide PHP runtime has following extensions and commands:

• The xmlextension.
• The zip extension.
• The curl extension.
• The mbstring extension.
• The unzip command is available.

It can use the php -m and which commands to check whether above requirements are installed and configured:

root@ubuntu-s-4vcpu-8gb-intel-sgp1-01:~/phpbrew# php -m | grep -i -E "xml|curl|zip|mbstring"
curl
libxml
mbstring
SimpleXML
xml
xmlreader
xmlwriter
zip
root@ubuntu-s-4vcpu-8gb-intel-sgp1-01:~/phpbrew# which unzip
/usr/bin/unzip

• Running the git clone https://github.com/phpbrew/phpbrew to clone the repository with the master branch.
• Downloading the composer.phar with the curl -sS https://getcomposer.org/installer | php command.
• Running the cd phpbrew/ to change the directory.
• Running the php ~/composer.phar install -n to install the required dependencies fir PHPBrew.
• Running the ./bin/phpbrew init to initialize the development PHPBrew version.
• Once modifying some changes in PHP codes, it should run above of two steps again to reinstall the new development PHPBrew version.