#include <stdlib.h>

       int system(const char *command);

       system()  executes a command specified in command by calling /bin/sh -c
       command, 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.

       The value returned is -1 on  error  (e.g.,  fork(2)  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 command 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.

       C89, C99, POSIX.1-2001.

       If  the  _XOPEN_SOURCE  feature test macro is defined (before including
       any header files), then the macros described in wait(2) (WEXITSTATUS(),
       etc.) are made available when including <stdlib.h>.

       As  mentioned, system() ignores SIGINT and SIGQUIT.  This may make pro-
       grams that call it from a loop uninterruptible, 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 set-user-ID or set-group-ID
       privileges, because strange values for some environment variables might
       be  used  to subvert system integrity.  Use the exec(3) family of func-
       tions instead, but not execlp(3) or execvp(3).  system() will  not,  in
       fact,  work  properly  from  programs  with set-user-ID or set-group-ID
       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.)

       In versions of glibc before 2.1.3, the check for  the  availability  of
       sh(1), signal(2), wait(2), exec(3)

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       be found at

                                  2010-09-10                         SYSTEM(3)
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