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

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  sys-
       tem()  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 priv-
       ileges,  because strange values for some environment vari-
       ables 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)

GNU                        11 May 1998                          1