system
Synopsis
#include <stdlib.h>
int system(const char *command);
Status
Partially implemented
Conformance
IEEE Std 1003.1-2017
Description
If command is a null pointer, the system() function shall determine whether the host environment has a command
processor. If command is not a null pointer, the system() function shall pass the string pointed to by command
to that command processor to be executed in an implementation-defined manner; this might then cause the program calling
system() to behave in a non-conforming manner or to terminate.
The
system() function shall behave as if a child process were created using fork(),
and the child process invoked the sh utility using execl() as follows:
execl(<shell path>, "sh", "-c", command, (char *)0);
Where <shell path> is an unspecified path name for the sh utility. It is
unspecified whether the handlers registered with pthread_atfork() are called
as part of the creation of the child process.
The system() function shall ignore the SIGINT and SIGQUIT signals, and shall block the SIGCHLD signal, while
waiting for the command to terminate. If this might cause the application to miss a signal that would have killed it,
then the application should examine the return value from system() and take whatever action is appropriate to the
application if the command terminated due to receipt of a signal.
The system() function shall not affect the termination status of any child of the calling processes other than the
process or processes it itself creates.
The system() function shall not return until the child process has terminated.
The system() function need not be thread-safe.
Return value
If command is a null pointer, system() shall return non-zero to indicate that a command processor is available, or
zero if none is available. The system() function shall always return non-zero when command is NULL.
If
command is not a null pointer, system() shall return the termination status of the command language interpreter in
the format specified by waitpid(). The termination status shall be as defined for
the sh utility; otherwise, the termination status is unspecified. If some error prevents
the command language interpreter from executing after the child process is created, the return value from system()
shall be as if the command language interpreter had terminated using exit(127) or _exit(127). If a child process
cannot be created, or if the termination status for the command language interpreter cannot be obtained, system()
shall return -1 and set errno to indicate the error.
Errors
The system() function may set errno values as described by fork().
In addition, system() may fail if:
ECHILD- The status of the child process created bysystem()is no longer available.
Tests
Untested
Known bugs
None