How to call External Procedure from Oracle Database

create a file which has name "shell.c"

content of shell.c file
------------------------------------
#include
#include
#include

void sh(char *);

void sh( char *cmd )
{
int num;

num = system(cmd);
}
------------------------------------

--create object file
[oracle@host01 lib]$  gcc -fPIC -g -c -Wall shell.c

--create shared library file
[oracle@host01 lib]$  gcc -shared -o shell.so shell.o


modify parameter in $ORACLE_HOME/hs/admin/extproc.ora file

SET EXTPROC_DLLS=/home/oracle/lib/shell.so

--create lib and procedure for test

CREATE OR REPLACE LIBRARY SHELL_LIB
 IS '/home/oracle/lib/shell.so'
/

CREATE OR REPLACE PROCEDURE "SHELL" (cmd IN char)
as external
name "sh"
library shell_lib
language C
parameters (cmd string);
/


SQL> exec shell('/bin/pwd > /home/oracle/lib/aa.txt');


output file looks like

[oracle@host01 lib]$ more aa.txt
/u01/oracle/11.2.0.3/dbs

ORA-28575: unable to open RPC connection to external procedure agent