System_Command is a commandline execution interface. Running functions from
the commandline can be risky if the proper precautions are not taken to
escape the shell arguments and reaping the exit status properly. This class
provides a formal interface to both, so that you can run a system command
as comfortably as you would run a php function, with full pear error
handling as results on failure. It is important to note that this class,
unlike other implementations, distinguishes between output to stderr and
output to stdout. It also reports the exit status of the command. So in
every sense of the word, it gives php shell capabilities.