SYSTEM(3)		  Linux Programmer's Manual		    SYSTEM(3)



NAME
       system - execute a shell command

SYNOPSIS
       #include 

       int system(const char *string);

DESCRIPTION
       system()	 executes a command specified in string by calling /bin/sh -c
       string, and returns after the command has been completed.  During exe-
       cution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT
       will be ignored.

RETURN VALUE
       The value returned is -1 on error (e.g. fork failed), and  the  return
       status  of the command otherwise.  This latter return status is in the
       format specified in wait(2).  Thus, the exit code of the command	 will
       be  WEXITSTATUS(status).	  In  case /bin/sh could not be executed, the
       exit status will be that of a command that does exit(127).

       If the value of string is NULL, system() returns nonzero if the	shell
       is available, and zero if not.

       system() does not affect the wait status of any other children.

CONFORMING TO
       ANSI C, POSIX.2, BSD 4.3

NOTES
       As mentioned, system() ignores SIGINT and SIGQUIT.  This may make pro-
       grams that call it from a loop uninterruptable, unless they take	 care
       themselves to check the exit status of the child. E.g.

	   while(something) {
	       int ret = system("foo");

	       if (WIFSIGNALED(ret) &&
		   (WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
		       break;
	   }

       Do  not	use  system()  from  a	program with suid or sgid privileges,
       because strange values for some environment variables might be used to
       subvert	system	integrity.   Use  the  exec(3)	family	of  functions
       instead, but not execlp(3) or execvp(3).	 system() will not, in	fact,
       work properly from programs with suid or sgid privileges on systems on
       which /bin/sh is bash version 2, since  bash  2	drops  privileges  on
       startup.	  (Debian  uses	 a  modified bash which does not do this when
       invoked as sh.)

       The check for the availability of /bin/sh is not	 actually  performed;
       it  is always assumed to be available.  ISO C specifies the check, but
       POSIX.2 specifies that the return shall always be  non-zero,  since  a
       system  without	the  shell  is not conforming, and it is this that is
       implemented.

       It is possible for the shell command to return 127, so  that  code  is
       not a sure indication that the execve() call failed.

SEE ALSO
       sh(1), signal(2), wait(2), exec(3)



				  2001-09-23			    SYSTEM(3)