debug drush (and php-cli)

Drush uses the cli version of php so traditional debugging tools and functions don't work.

// add --debug to the end of a drush command
drush vget site_name --debug
 
// output a message to the screen
drush_log("my message");
 
// get information over the php version (php_info)
drush php-eval "phpinfo();" | less
 
// to debug an aegir command
// /usr/bin/php /opt/drush/drush.php --php='/usr/bin/php' --root='/var/aegir/platforms/drupal-7.22' provision-save '@platform_drupal722' --backend 2>&1
/usr/bin/php /opt/drush/drush.php --php='/usr/bin/php' --root='/var/aegir/platforms/drupal-7.22' provision-save '@platform_drupal722' --debug

Display errors - WSOD

The bootstrap override the values you could set to display error ad the reporting level. To be 100% sure everything is printed out when something fails in a blank screen (wsod), make index.php like this:

Properly render a field

Drupal offers a few (sometimes complicated...) solutions to output a field. Lets take an example with a date field.
To display the full rendered field: field_view_field()