system(3S)

DESCRIPTION

system() executes the command specified by the string pointed to by command. The environment of the executed command is as if a child process were created using fork() (see fork(2)), and the child process invoked the sh-posix(1) utility via a call to execl() (see exec(2)) as follows:

system() ignores the SIGINT and SIGQUIT signals, and blocks 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, 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.

system() does not affect the termination status of any child of the calling processes other than the process or processes it itself creates.

system() does not return until the child process has terminated.

APPLICATION USAGE

The interface system() is thread-safe. It is not async-cancel-safe. A cancellation point may occur when a thread is executing system().

If the return value of system() is not -1, its value can be decoded through the use of the macros described in <sys/wait.h>. For convenience, these macros are also provided in <stdlib.h>.

Note that, while system() must ignore SIGINT and SIGQUIT and block SIGCHLD while waiting for the child to terminate, the handling of signals in the executed command is as specified by fork(2) and exec(2). For example, if SIGINT is being caught or is set to SIG_DFL when system() is called, the child is started with SIGINT handling set to SIG_DFL.

Ignoring SIGINT and SIGQUIT in the parent process prevents coordination problems (such as two processes reading from the same terminal) when the executed command ignores or catches one of the signals.

RETURN VALUE

If command is null, system() returns non-zero.

If command is not null, system() returns the termination status of the command language interpreter in the format specified by wait(2). The termination status of the command language interpreter is as specified for sh-posix(1), except that if some error prevents the command language interpreter from executing after the child process is created, the return value from system() is as if the command language interpreter had terminated using _exit(127). If a child process cannot be created, or if the termination status for the command language interpreter cannot be obtained, system() returns -1 and sets errno to indicate the error.

DIAGNOSTICS

system() forks to create a child process which, in turn, exec()s /usr/bin/sh in order to execute string. If the fork fails, system() returns -1 and sets errno. If the exec fails, system() returns the status value returned by waitpid() (see wait(2)) for a process that terminates with a call of exit(127).

ERRORS

If errors are encountered, system() sets errno values as described by fork(2).

FILES

/usr/bin/sh

SEE ALSO

sh(1), fork(2), exec(2), wait(2).

STANDARDS CONFORMANCE

system(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2, ANSI C