#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 -1 on error (e.g. fork failed),
and the return status of the command otherwise.
This latter return status is in the format
specified in wait(2) . Thus, the exit code of the command will be WEXITSTATUS(status) . In case /bin/sh could not be executed, the exit status will be that of
a command that does exit(127) .
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
NOTES
As mentioned, system() ignores SIGINT and SIGQUIT. This may make programs that call it
from a loop uninterruptable, 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 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.