First, the simplest way to install Grav is with the pre-built package, as it contains everything you need, just unzip and point your browser at it. Those are available in the downloads site or in the “releases” tab of github.
Second, a parse error usually means an older version of PHP. Can you confirm you are running PHP 5.6 as you say? just type php -v from your terminal.
If you look at line 13 of bin/grav you will see it just says: use Grav\Common\Composer;
@rhukster, Originally php -v results 5.2 version (only CLI, phpinfo gives me PHP Version 5.6.5-pl0-gentoo). but my hosting provider recommend me to use these commands to change it:
echo “alias php=/usr/lib64/php5.6/bin/php” > ~/.bashrc
source ~/.bashrc
But bin/grav list command (for example) gives me the same old error (trying on zipped version now). Its strange!