Originální popis anglicky:
system - execute a shell command
Návod, kniha: Linux Programmer's Manual
#include <stdlib.h>
int system(const char *string);
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.
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.
ANSI C, POSIX.2, BSD 4.3
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.
sh(1),
signal(2),
wait(2),
exec(3)
