And you can also create a unix command parameter in SM69 and use it in FM SXPG_COMMAND_EXECUTE.
You can find a step by step approach here: http://wiki.scn.sap.com/wiki/display/ABAP/Creation+of+External+Commands+with+the+help+of+UNIX+Coding+in+SAP
Although you might have to change the command as the one in tutorial is for listing the files in a directory.
Best Regards,
Kush