• Use the DBMS_SCHEDULER package
• Run a Java method to execute your command.
• Run a C program to execute your command.

DBMS_SCHEDULER offers the simplest and most intuitive solution, especially from the standpoint of DBA and system administration tasks. I talk about this solution on the OTN Best Practice page:

http://apex.oracle.com/pls/otn/f?p=2853:4:1544539351000407::NO::P4_QA_ID:16282

I will, in this Toad World blog, offer brief guidance on the other two options. It is very unlikely that you will be able to rely solely on the content below to implement either approach. Instead, I suggest you use this as a starting point and then from there visit the detailed Oracle documentation and/or the full chapter coverage of both these techniques in my Oracle PL/SQL Programming.

1. Find the Java class that implements host command execution.
2. Build a class that invokes that host command method. Let's call it HostCommand.
3. Build a PL/SQL program that calls a method in HostCommand to run your command.
4. Acquire the privileges needed to execute host commands via Java in the database.

Let's go through each of these steps.

1. Find the Java class that implements host command execution.
   
   Objects of the java.lang.Runtime class include an exec method that will execute a host command.
    
2. Build a class that invokes that host command method. Let's call it HostCommand.
   
   Here's code to create a new Java class in the database to invoke this command for the Windows XP operating system:
   
   CREATE OR REPLACE AND RESOLVE JAVA SOURCE NAMED "UTLcmd"
   AS import java.lang.Runtime;
   
   public class execHostCommand
   {
     public static void execute (String command)
       throws java.io.IOException
     {
      String osName = System.getProperty("os.name");
      if(osName.equals("Windows XP"))
          command = "cmd /c " + command;
      Runtime rt = java.lang.Runtime.getRuntime();
      rt.exec(command);
     }
   }
   /
   
   You can easily modify the execute method to support other operating systems based on the value of osName.
    
3. Build a PL/SQL program that calls a method in HostCommand to run your command.
   
   CREATE OR REPLACE PACKAGE host_command IS
     PROCEDURE execute (cmd IN VARCHAR2) AS LANGUAGE JAVA NAME
              'execHostCommand.execute(java.lang.String)';
   END;
   /
    
   Notice that I "map" the VARCHAR2 datatype to the java.lang.String class in my call to the new Java method.
    
4. Acquire the privileges needed to execute host commands via Java in the database.
    
   You need special privileges to execute host commands from within the database through Java. Otherwise when you try to execute your command you will see an error like this (the error message will vary depending on what you are trying to do):
    
   
    
   One way to obtain these privileges to have the JAVASYSPRIV role granted to your schema. This role contains all the privileges you need (and more).
    
   For a more nuanced approach to granting the required privileges, you can also use the Java security API available in the Oracle database. For example, if I want to delete a file using a host command (perhaps it is not accessible through UTL_FILE), I will need to grant the following privileges to the schema in which the command is executed, such as HR:
   
   BEGIN
      DBMS_JAVA.grant_permission ('HR'
                                , 'SYS:java.io.FilePermission'
                                , '<>'
                                , 'execute'
                                 );
      DBMS_JAVA.grant_permission ('HR'
                                , 'SYS:java.lang.RuntimePermission'
                                , 'writeFileDescriptor'
                                , ''
                                 );
      DBMS_JAVA.grant_permission ('HR'
                                , 'SYS:java.lang.RuntimePermission'
                                , 'readFileDescriptor'
                                , ''
                                 );
   END;
   /

1. Find (or build) the C program that implements host command execution.
2. Save the C source to a file and generate a shared library for it.
3. Save the library file where Oracle can find it.
4. Define a library inside Oracle that is associated with the shared library on disk.
5. Create a PL/SQL wrapper for the C function.

Let's go through each of these steps.

1. Find (or build) the C program that implements host command execution.
    
   The C system function executes an operating system command. So I build a simple C function, extprocsh(), that accepts a string and passes it to the system function for execution:
    
   int extprocsh(char *cmd)
   {
      return system(cmd);
   }
    
   The function returns the result code as provided by system, a function normally found in the C runtime library (libc) on Unix, or in msvcrt.dll on Microsoft platforms.
    
2. Save the C source to a file and generate a shared library for it.
    
   I save the source code in a file named extprocsh.c. I then use the GNU C compiler to generate a shared library. On a 64-bit Solaris machine running GCC 3.4.2 and Oracle Database 10g Release 2, the following compiler command worked to create a shared library:
    
   gcc -m64 extprocsh.c -fPIC -G -o extprocsh.so
    
   Similarly, on Microsoft Windows XP Pro running GCC 3.2.3 from Minimal GNU for Windows (MinGW), also with Oracle Database 10g Release 2, this works:
    
   c:\MinGW\bin\gcc extprocsh.c -shared -o extprocsh.dll
    
3. Save the library file where Oracle can find it.
    
   These commands generate a shared library file, extprocsh.so or extprocsh.dll. Now I need to put the library file somewhere that Oracle can find it. The default locations for Windows and Unix respectively are:
    
   $ORACLE_HOME/bin
   $ORACLE_HOME/lib
    
   If you want to use a non-default location, you will need to edit the listener configuration file and supply path value(s) for the ENVS="EXTPROC_DLLS...".
    
4. Define a library inside Oracle that is associated with the shared library on disk.
    
   After copying the file and/or making adjustments to the listener, you will then define a "library" inside Oracle to point to the DLL. For example:
    
   CREATE OR REPLACE LIBRARY extprocshell_lib 
      AS '/u01/app/oracle/local/lib/extprocsh.so';   -- Unix
        
   CREATE OR REPLACE LIBRARY extprocshell_lib
      AS 'c:\oracle\local\lib\extprocsh.dll';      -- Microsoft
    
   Note: performing this step requires Oracle’s CREATE LIBRARY privilege.
    
5. Create a PL/SQL wrapper for the C function.
    
   Now I can create a PL/SQL call specification which uses the newly created library:
    
   CREATE OR REPLACE FUNCTION exec_host_command (cmd IN VARCHAR2)
      RETURN PLS_INTEGER
   AS
      LANGUAGE C
      LIBRARY extprocshell_lib
      NAME "extprocsh"
      PARAMETERS (cmd STRING, RETURN INT);

   Then, assuming that your DBA has set up the system environment to support external procedures, the exec_host_command function can now be called anywhere you can invoke a PL/SQL function. 

   Note that these operating system commands will execute with the same privileges as the Oracle Net listener that spawns the extproc process.