Daftar Isi

• ioctl FILEHANDLE,FUNCTION,SCALAR

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

   require "sys/ioctl.ph";  # probably in $Config{archlib}/sys/ioctl.ph
   

  to get the correct function definitions. If sys/ioctl.ph doesn'texist or doesn't have the correct definitions you'll have to roll yourown, based on your C header files such as <sys/ioctl.h>.(There is a Perl script called h2ph that comes with the Perl kit thatmay help you in this, but it's nontrivial.) SCALAR will be read and/orwritten depending on the FUNCTION; a C pointer to the string value of SCALARwill be passed as the third argument of the actual ioctl call. (If SCALARhas no string value but does have a numeric value, that value will bepassed rather than a pointer to the string value. To guarantee this to betrue, add a 0 to the scalar before using it.) The pack and unpackfunctions may be needed to manipulate the values of structures used byioctl.

  The return value of ioctl (and fcntl) is as follows:

   if OS returns:  then Perl returns:
   
   -1   undefined value
   
   0  string "0 but true"
   
   anything else   that number
   

  Thus Perl returns true on success and false on failure, yet you canstill easily determine the actual value returned by the operatingsystem:

   $retval = ioctl(...) || -1;
   
   printf "System returned %d\n", $retval;
   

  The special string "0 but true" is exempt from -w complaintsabout improper numeric conversions.

  Portability issues: ioctl in perlport.