Fcntl

Fcntl loads the constants defined in the system’s <fcntl.h> C header file, and used with both the fcntl(2) and open(2) POSIX system calls.

To perform a fcntl(2) operation, use IO::fcntl.

To perform an open(2) operation, use IO::sysopen.

The set of operations and constants available depends upon specific operating system. Some values listed below may not be supported on your system.

See your fcntl(2) man page for complete details.

Open /tmp/tempfile as a write-only file that is created if it doesn’t exist:

require 'fcntl'

fd = IO.sysopen('/tmp/tempfile',
                Fcntl::O_WRONLY | Fcntl::O_EXCL | Fcntl::O_CREAT)
f = IO.open(fd)
f.syswrite("TEMP DATA")
f.close

Get the flags on file s:

m = s.fcntl(Fcntl::F_GETFL, 0)

Set the non-blocking flag on f in addition to the existing flags in m.

f.fcntl(Fcntl::F_SETFL, Fcntl::O_NONBLOCK|m)

Constants

F_ALLOCATEALL

macOS specific flag used with F_PREALLOCATE for allocating all contiguous space or no space.

F_ALLOCATECONTIG

macOS specific flag used with F_PREALLOCATE for allocating contiguous space.

F_ALLOCATEPERSIST

macOS specific flag used with F_PREALLOCATE. Allocate space that is not freed when close is called.

FD_CLOEXEC

the value of the close-on-exec flag.

F_DUP2FD

It is a FreeBSD specific constant and equivalent to dup2 call.

F_DUP2FD_CLOEXEC

It is a FreeBSD specific constant and acts similarly as F_DUP2FD but set the FD_CLOEXEC flag in addition.

F_DUPFD

Duplicate a file descriptor to the minimum unused file descriptor greater than or equal to the argument.

The close-on-exec flag of the duplicated file descriptor is set. (Ruby uses F_DUPFD_CLOEXEC internally if available to avoid race condition. F_SETFD is used if F_DUPFD_CLOEXEC is not available.)