открыть файл (open file)
Использование в приложениях (Application usage)
POSIX.1‐2008 does not require that terminal parameters be
automatically set to any state on first open, nor that they be
reset after the last close. It is possible for a non-conforming
application to leave a terminal device in a state where the next
process to use that device finds it in a non-conforming state,
but has no way of determining this. To ensure that the device is
set to a conforming initial state, applications which perform a
first open of a terminal (other than a pseudo-terminal) should do
so using the O_TTY_INIT flag to set the parameters associated
with the terminal to a conforming state.
Except as specified in this volume of POSIX.1‐2017, the flags
allowed in oflag are not mutually-exclusive and any number of
them may be used simultaneously. Not all combinations of flags
make sense. For example, using O_SEARCH | O_CREAT will
successfully open a pre-existing directory for searching, but if
there is no existing file by that name, then it is unspecified
whether a regular file will be created. Likewise, if a non-
directory file descriptor is successfully returned, it is
unspecified whether that descriptor will have execute permissions
as if by O_EXEC (note that it is unspecified whether O_EXEC and
O_SEARCH have the same value).
