newlib/libc/stdlib/system.c

   1 /*
   2 FUNCTION
   3 <<system>>---execute command string
   4
   5 INDEX
   6         system
   7 INDEX
   8         _system_r
   9
  10 SYNOPSIS
  11         #include <stdlib.h>
  12         int system(char *<[s]>);
  13
  14         int _system_r(void *<[reent]>, char *<[s]>);
  15
  16 DESCRIPTION
  17
  18 Use <<system>> to pass a command string <<*<[s]>>> to <</bin/sh>> on
  19 your system, and wait for it to finish executing.
  20
  21 Use ``<<system(NULL)>>'' to test whether your system has <</bin/sh>>
  22 available.
  23
  24 The alternate function <<_system_r>> is a reentrant version.  The
  25 extra argument <[reent]> is a pointer to a reentrancy structure.
  26
  27 RETURNS
  28 <<system(NULL)>> returns a non-zero value if <</bin/sh>> is available, and
  29 <<0>> if it is not.
  30
  31 With a command argument, the result of <<system>> is the exit status
  32 returned by <</bin/sh>>.
  33
  34 PORTABILITY
  35 ANSI C requires <<system>>, but leaves the nature and effects of a
  36 command processor undefined.  ANSI C does, however, specify that
  37 <<system(NULL)>> return zero or nonzero to report on the existence of
  38 a command processor.
  39
  40 POSIX.2 requires <<system>>, and requires that it invoke a <<sh>>.
  41 Where <<sh>> is found is left unspecified.
  42
  43 Supporting OS subroutines required: <<_exit>>, <<_execve>>, <<_fork_r>>,
  44 <<_wait_r>>.
  45 */
  46
  47 #include <_ansi.h>
  48 #include <errno.h>
  49 #include <stddef.h>
  50 #include <stdlib.h>
  51 #include <unistd.h>
  52 #include <_syslist.h>
  53 #include <reent.h>
  54
  55 #if defined (unix) || defined (__CYGWIN__)
  56 static int do_system (struct _reent *ptr, const char *s);
  57 #endif
  58
  59 int
  60 _system_r (struct _reent *ptr,
  61      const char *s)
  62 {
  63 #if defined(HAVE_SYSTEM)
  64   return _system (s);
  65   ptr = ptr;
  66 #elif defined(NO_EXEC)
  67   if (s == NULL)
  68     return 0;
  69   errno = ENOSYS;
  70   return -1;
  71 #else
  72
  73   /* ??? How to handle (s == NULL) here is not exactly clear.
  74      If _fork_r fails, that's not really a justification for returning 0.
  75      For now we always return 0 and leave it to each target to explicitly
  76      handle otherwise (this can always be relaxed in the future).  */
  77
  78 #if defined (unix) || defined (__CYGWIN__)
  79   if (s == NULL)
  80     return 1;
  81   return do_system (ptr, s);
  82 #else
  83   if (s == NULL)
  84     return 0;
  85   errno = ENOSYS;
  86   return -1;
  87 #endif
  88
  89 #endif
  90 }
  91
  92 #ifndef _REENT_ONLY
  93
  94 int
  95 system (const char *s)
  96 {
  97   return _system_r (_REENT, s);
  98 }
  99
 100 #endif
 101 \f
 102 #if defined (unix) && !defined (__CYGWIN__) && !defined(__rtems__)
 103 extern char **environ;
 104
 105 /* Only deal with a pointer to environ, to work around subtle bugs with shared
 106    libraries and/or small data systems where the user declares his own
 107    'environ'.  */
 108 static char ***p_environ = &environ;
 109
 110 static int
 111 do_system (struct _reent *ptr,
 112      const char *s)
 113 {
 114   char *argv[4];
 115   int pid, status;
 116
 117   argv[0] = "sh";
 118   argv[1] = "-c";
 119   argv[2] = (char *) s;
 120   argv[3] = NULL;
 121
 122   if ((pid = _fork_r (ptr)) == 0)
 123     {
 124       _execve ("/bin/sh", argv, *p_environ);
 125       exit (100);
 126     }
 127   else if (pid == -1)
 128     return -1;
 129   else
 130     {
 131       int rc = _wait_r (ptr, &status);
 132       if (rc == -1)
 133         return -1;
 134       status = (status >> 8) & 0xff;
 135       return status;
 136     }
 137 }
 138 #endif
 139
 140 #if defined (__CYGWIN__)
 141 static int
 142 do_system (struct _reent *ptr,
 143      const char *s)
 144 {
 145   char *argv[4];
 146   int pid, status;
 147
 148   argv[0] = "sh";
 149   argv[1] = "-c";
 150   argv[2] = (char *) s;
 151   argv[3] = NULL;
 152
 153   if ((pid = vfork ()) == 0)
 154     {
 155       /* ??? It's not clear what's the right path to take (pun intended :-).
 156          There won't be an "sh" in any fixed location so we need each user
 157          to be able to say where to find "sh".  That suggests using an
 158          environment variable, but after a few more such situations we may
 159          have too many of them.  */
 160       char *sh = getenv ("SH_PATH");
 161       if (sh == NULL)
 162         sh = "/bin/sh";
 163       _execve (sh, argv, environ);
 164       exit (100);
 165     }
 166   else if (pid == -1)
 167     return -1;
 168   else
 169     {
 170       extern int _wait (int *);
 171       int rc = _wait (&status);
 172       if (rc == -1)
 173         return -1;
 174       status = (status >> 8) & 0xff;
 175       return status;
 176     }
 177 }
 178 #endif