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`system'--execute command string

     #include <stdlib.h>
     int system(char *S);
     int _system_r(void *REENT, char *S);
Use `system' to pass a command string `*S' to `/bin/sh' on your system,
and wait for it to finish executing.
   Use "`system(NULL)'" to test whether your system has `/bin/sh'
   The alternate function `_system_r' is a reentrant version.  The
extra argument REENT is a pointer to a reentrancy structure.
`system(NULL)' returns a non-zero value if `/bin/sh' is available, and
`0' if it is not.
   With a command argument, the result of `system' is the exit status
returned by `/bin/sh'.
ANSI C requires `system', but leaves the nature and effects of a
command processor undefined.  ANSI C does, however, specify that
`system(NULL)' return zero or nonzero to report on the existence of a
command processor.
   POSIX.2 requires `system', and requires that it invoke a `sh'.
Where `sh' is found is left unspecified.
   Supporting OS subroutines required: `_exit', `_execve', `_fork_r',