fcntl

• fcntl FILEHANDLE,FUNCTION,SCALAR

  Implements the fcntl(2) function. You'll probably have to say

      use Fcntl;

  first to get the correct constant definitions. Argument processing and value returned work just like ioctl below. For example:

      use Fcntl;
      my $flags = fcntl($filehandle, F_GETFL, 0)
          or die "can't fcntl F_GETFL: $!";

  You don't have to check for defined on the return from fcntl. Like ioctl, it maps a return from the system call into "0 but true" in Perl. This string is true in boolean context and in numeric context. It is also exempt from the normal -w warnings on improper numeric conversions.

  Note that fcntl raises an exception if used on a machine that doesn't implement fcntl(2). See the Fcntl module or your fcntl(2) manpage to learn what functions are available on your system.

  Here's an example of setting a filehandle named REMOTE to be non-blocking at the system level. You'll have to negotiate $| on your own, though.

      use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);
      $flags = fcntl(REMOTE, F_GETFL, 0)
                  or die "Can't get flags for the socket: $!\n";
      $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
                  or die "Can't set flags for the socket: $!\n";

  Portability issues: fcntl in perlport.