Provided by: manpages-pt-dev_20040726-4_all bug

NAME

       system - execute a shell command

SYNOPSIS

       #include <stdlib.h>

       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
       execution  of  the  command,  SIGCHLD  will  be blocked, and SIGINT and
       SIGQUIT will be ignored.

RETURN VALUE

       The value returned is 127 if the execve() call for /bin/sh fails, -1 if
       there was another error and the return code of the command otherwise.

       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

BUGS

       It is extremely unfortunate that the libc version of  system()  ignores
       interrupts.    This   makes   programs   that   call  it  from  a  loop
       uninterruptable.  This means that for such purposes one should not  use
       system() but a private version like (warning: untested code!)

       int my_system (const char *command) {
           int pid, status;

           if (command == 0)
               return 1;
           pid = fork();
           if (pid == -1)
               return -1;
           if (pid == 0) {
               char *argv[4];
               argv[0] = "sh";
               argv[1] = "-c";
               argv[2] = command;
               argv[3] = 0;
               execve("/bin/sh", argv, environ);
               exit(127);
           }
           do {
               if (waitpid(pid, &status, 0) == -1) {
                   if (errno != EINTR)
                       return -1;
               } else
                   return status;
           } while(1);
       }

       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; check errno to make
       sure.

SEE ALSO

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