Fcntl (Programming Perl)

32.17. Fcntl

use Fcntl;              # Import standard fcntl.h constants.
use Fcntl ":flock";     # Import LOCK_* constants.
use Fcntl ":seek";      # Import SEEK_CUR, SEEK_SET, SEEK_END.
use Fcntl ":mode";      # Import S_* stat checking constants.
use Fcntl ":Fcompat";   # Import F* constants.

The Fcntl module provides constants for use with various Perl built-in functions. The default set of imports includes constants like F_GETFL and F_SETFL for fcntl, SEEK_SET and SEEK_END for seek and sysseek, and O_CREAT and O_EXCL for sysopen. Supported import tags include ":flock" to access the LOCK_EX, LOCK_NB, LOCK_SH, and LOCK_UN constants for flock; ":mode" to get at constants from sys/stat.h like S_IRUSR and S_ISFIFO; ":seek" to get at the three arguments for seek and sysseek; and ":Fcompat" to get the old-style symbols with a leading "F" but not "F_", like FAPPEND, FASYNC, and FNONBLOCK. See the online documentation for the Fcntl module and your operating system's documentation on the relevant syscalls, like fcntl(2), lseek(2), open(2), and stat(2).