File control system call

Daftar Isi

• 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 andvalue returned work 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 fcntl.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 0in numeric context. It is also exempt from the normal -w warningson improper numeric conversions.

  Note that fcntl raises an exception if used on a machine thatdoesn'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 benon-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.