-  unix(+Action)
 - This predicate provides a partial emulation of the corresponding
Quintus predicate. It provides access to some operating system
features and unlike the name suggests, is not operating system
specific. Defined actions are below.
- system(+Command)
 - Equivalent to 
shell(Command) 
- shell(+Command)
 - Equivalent to 
shell(Command) 
- access(File,0)
 - Equivalent to 
access_file(File, read) 
- cd(Dir)
 - Equivalent to 
working_directory(_, Dir) 
- args(List)
 - Equivalent to 
current_prolog_flag(os_argv, List). 
- argv(List)
 - Equivalent to 
args(List), but arguments that are syntactically
valid numbers are passed as a number.