How forbid use fork() in exec() program.

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system

system(3S)																system(3S)

NAME

       system() - issue a shell command

SYNOPSIS

DESCRIPTION

       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 (see fork(2)), and the child process invoked the sh-posix(1) utility via a call to (see exec(2)) as follows:

       ignores the and signals, and blocks the 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 and take whatever action is appropriate to the
       application if the command terminated due to receipt of a signal.

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

       does not return until the child process has terminated.

APPLICATION USAGE

       If the return value of is not -1, its value can be decoded through the use of the macros described in For  convenience,	these  macros  are
       also provided in

       Note  that, while must ignore and and block 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 is being caught or is set to when is called, the child is started with handling set to

       Ignoring and 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, returns non-zero.

       If  command is not null, returns the termination status of the command language interpreter in the format specified by wait(2).	The termi-
       nation 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 is as if the command language interpreter had termi-
       nated using If a child process cannot be created, or if the termination status for the command language	interpreter  cannot  be  obtained,
       returns -1 and sets to indicate the error.

DIAGNOSTICS

       forks  to  create  a  child  process which, in turn, in order to execute string.  If the fork fails, returns -1 and sets If the exec fails,
       returns the status value returned by (see wait(2)) for a process that terminates with a call of

ERRORS

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

FILES

SEE ALSO

       sh(1), fork(2), exec(2), wait(2), thread_safety(5).

STANDARDS CONFORMANCE

																	system(3S)

Programming