# module 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

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.)

F_GETFD

  Read the close-on-exec flag of a file descriptor.

F_GETFL

  Get the file descriptor flags. This will be one or more of the O_* flags.

F_GETLK

  Determine whether a given region of a file is locked. This uses one of the F_*LK flags.

F_GETPIPE_SZ

  Return (as the function result) the capacity of the pipe referred to by fd.

F_RDLCK

  Read lock for a region of a file

F_SETFD

  `Set` the close-on-exec flag of a file descriptor.

F_SETFL

  `Set` the file descriptor flags. This will be one or more of the O_* flags.

F_SETLK

  Acquire a lock on a region of a file. This uses one of the F_*LCK flags.

F_SETLKW

  Acquire a lock on a region of a file, waiting if necessary. This uses one of the F_*LCK flags

F_SETPIPE_SZ

  Change the capacity of the pipe referred to by fd to be at least arg bytes.

F_UNLCK

  Remove lock for a region of a file

F_WRLCK

  Write lock for a region of a file

O_ACCMODE

  Mask to extract the read/write flags

O_APPEND

  Open the file in append mode

O_CREAT

  Create the file if it doesn’t exist

O_EXCL

  Used with `O_CREAT`, fail if the file exists

O_NDELAY

  Open the file in non-blocking mode

O_NOCTTY

  Open TTY without it becoming the controlling TTY

O_NONBLOCK

  Open the file in non-blocking mode

O_RDONLY

  Open the file in read-only mode

O_RDWR

  Open the file in read-write mode

O_TRUNC

  Truncate the file on open

O_WRONLY

  Open the file in write-only mode.

VERSION

  The version string.