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

       system - execute a shell command

       #include <stdlib.h>

       int system(const char *string);

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

       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 exe-
       cuted, 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.

       ANSI C, POSIX.2, BSD 4.3

       As  mentioned,  system()  ignores SIGINT and SIGQUIT.  This may make programs 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))

       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.

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

					    2001-09-23					SYSTEM(3)
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