I tried to install yaml by using this commands
sudo apt-get install php-pear libyaml-dev
sudo pecl install yaml
But this YAML requires php7.0 and newer version. I use PHP 5.5.9 How can install older version of YAML.
You should change your package repository (For example in Debian/Ubuntu Aptitude repositories), for PHP5 versions and then install that version or YAML.
You can use also Composer for the dependencies management, or the "hardest" way, download the source code and implement by yourself.
echo "deb http://packages.dotdeb.org wheezy-php56 all" >> /etc/apt/sources.list.d/dotdeb.list
echo "deb-src http://packages.dotdeb.org wheezy-php56 all" >> /etc/apt/sources.list.d/dotdeb.list
wget http://www.dotdeb.org/dotdeb.gpg -O- |apt-key add -
apt-get update
apt-get install php-pearl ....