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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

FD_CLOEXEC

the value of the close-on-exec flag.

F_DUPFD

F_DUPFD

Duplicate a file descriptor to the mimimum 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

F_GETFD

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

F_GETFL

F_GETFL

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

F_GETLK

F_GETLK

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

F_RDLCK

F_RDLCK

Read lock for a region of a file

F_SETFD

F_SETFD

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

F_SETFL

F_SETFL

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

F_SETLK

F_SETLK

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

F_SETLKW

F_SETLKW

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

F_UNLCK

F_UNLCK

Remove lock for a region of a file

F_WRLCK

F_WRLCK

Write lock for a region of a file

O_ACCMODE

O_ACCMODE

Mask to extract the read/write flags

O_APPEND

O_APPEND

Open the file in append mode

O_CREAT

O_CREAT

Create the file if it doesn't exist

O_EXCL

O_EXCL

Used with O_CREAT, fail if the file exists

O_NDELAY

O_NDELAY

Open the file in non-blocking mode

O_NOCTTY

O_NOCTTY

Open TTY without it becoming the controlling TTY

O_NONBLOCK

O_NONBLOCK

Open the file in non-blocking mode

O_RDONLY

O_RDONLY

Open the file in read-only mode

O_RDWR

O_RDWR

Open the file in read-write mode

O_TRUNC

O_TRUNC

Truncate the file on open

O_WRONLY

O_WRONLY

Open the file in write-only mode.

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