#include <stdlib.h> int system(const char *command);
If the value of command is NULL, system() returns non-zero if the shell is available, and zero if not.
system() does not affect the wait status of any other children.
If the _XOPEN_SOURCE feature test macro is defined, 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 programs 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))
break;
}
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 functions 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 /bin/sh was not actually performed if command was NULL; instead it was always assumed to be available, and system() always returned 1 in this case. Since glibc 2.1.3, this check is performed because, even though POSIX.1-2001 requires a conforming implementation to provide a shell, that shell may not be available or executable if the calling program has previously called chroot(2) (which is not specified by POSIX.1-2001).
It is possible for the shell command to return 127, so that code is not a sure indication that the execve(2) call failed.