Fcntl - load the C Fcntl.h defines
use Fcntl;
use Fcntl qw(:DEFAULT :flock);This module is just a translation of the C fnctl.h file. Unlike the old mechanism of requiring a translated fnctl.ph file, this uses the h2xs program (see the Perl source distribution) and your native C compiler. This means that it has a far more likely chance of getting the numbers right.
Only #define symbols get translated; you must still correctly pack up your own arguments to pass as args for locking functions, etc.
By default your system's F_* and O_* constants (eg, F_DUPFD and O_CREAT) and the FD_CLOEXEC constant are exported into your namespace.
You can request that the flock() constants (LOCK_SH, LOCK_EX, LOCK_NB and LOCK_UN) be provided by using the tag :flock. See Exporter.
You can request that the old constants (FAPPEND, FASYNC, FCREAT, FDEFER, FEXCL, FNDELAY, FNONBLOCK, FSYNC, FTRUNC) be provided for compatibility reasons by using the tag :Fcompat. For new applications the newer versions of these constants are suggested (O_APPEND, O_ASYNC, O_CREAT, O_DEFER, O_EXCL, O_NDELAY, O_NONBLOCK, O_SYNC, O_TRUNC).
For ease of use also the SEEK_* constants (for seek() and sysseek(), e.g. SEEK_END) and the S_I* constants (for chmod() and stat()) are available for import. They can be imported either separately or using the tags :seek and :mode.
Please refer to your native fcntl(2), open(2), fseek(3), lseek(2) (equal to Perl's seek() and sysseek(), respectively), and chmod(2) documentation to see what constants are implemented in your system.
See perlopentut to learn about the uses of the O_* constants with sysopen().
See "seek" in perlfunc and "sysseek" in perlfunc about the SEEK_* constants.
See "stat" in perlfunc about the S_I* constants.