Drush 8 throws unknown error on Drupal 8 install UPDATE: I have managed to update Drush using Wim Mostrey's help as seen below. Drush is now at version 8, and continues to work with my Drupal 7 sites, but when I try to use it on my Drupal 8 site, I get this:

Drush command terminated abnormally due to an unrecoverable error.  
Error: syntax error, unexpected 'class' (T_CLASS), expecting identifier (T_STRING) or variable (T_VARIABLE) or '{' or '$' in /home1/[uname]/public_html/_d8/core/lib/Drupal/Component/Ser‌​ialization/Yaml.php, line 54 Parse error: syntax error, unexpected 'class' (T_CLASS), expecting identifier (T_STRING) or variable (T_VARIABLE) or '{' or '$' in /home1/[uname]/public_html/_d8/core/lib/Drupal/Component/Ser‌​ialization/Yaml.php


Does anyone know what this issue is?



Original Question: I want to upgrade from Drush 6.5 to 8, even though current Drush is ver 9 because I want to keep backwards compat. I'm not understanding the instructions on github very well, and concerned about it getting gummed up. Is there a clear, simple guide for this?
Looks like the version of PHP you are using does not meet the minimum requirements for Drush and/or Drupal.  Check your PHP version, and compare against the Drush supported versions matrix.