Lookup using PlsExtProc to call a registered library. This allows your PL/SQL program to call external programs directly, provided they are registered with your database. There's a known security hole related to ExtProc, so checkout Oracle Metalink for more info.
A poor man's alternative is to use the UTL_FILE package to write your commands to a text file on the server, such as a file named my_commands.bat on Windows. Then use Windows Task Scheduler to run that file periodically. Nearly identical solution on Solaris.