How to read input username to drush script? I need to complete a script  which gets a username from terminal to a php script and then deletes the user's comments. 

So I am wondering how the username should be read by the php script, the same way that one can read a value in a bash script. 

Thanks
In your Drush command you need to call drush_get_option('myoption'); to get the value of an input parameter. 

To call your Drush command you need to specify your input option as below:

drush mycommand --myoption=myvalue