See the current Perl documentation for fcntl.
Here is our local, out-dated (pre-5.6) version:
fcntl - file control system all
fcntl(2) function. You'll
probably have to say
first to get the correct constant definitions. Argument processing and value return works just like ioctl() below. For example:
use Fcntl; fcntl($filehandle, F_GETFL, $packed_return_buffer) or die "can't fcntl F_GETFL: $!";
You don't have to check for defined() on the return from
fnctl(). Like ioctl(), it maps a
0 return from the system call into ``
0 but true'' in Perl. This string is true in boolean context and
0 in numeric context. It is also exempt from the normal -w warnings on improper numeric conversions.
Note that fcntl() will produce a fatal error if used on a machine that doesn't implement