I am trying to get the current number of rows and columns of the TTY I am attached to under linux.

Originally, I was calling the "/bin/stty size" prog and grabbing the output, but decided I didn't want to have to call an outside program.

I looked at the source of 'stty', and found it using the TIOCGWINSZ call to 'ioctl' on stdout and getting back a struct of 4 shorts (16-bit).

So, converting that to perl, I end up with: 

#!/usr/bin/perl -w
use strict;

my $need_update;
my ($maxcols, $maxrows);

sub getwinsize () {

  sub TIOCGWINSZ () {0x5413}  #from ioctls.ph, which wouldn't include

  return ($maxcols,$maxrows) if $maxcols && $maxrows && !$need_update;

  my $winsize=0;
  my $err = ioctl (STDOUT, TIOCGWINSZ, $winsize);
  if ($err) {
    print "ioctl err: $?\n";
  }

  my ($rows, $cols, $xpix, $ypix) = unpack "s!*", $winsize;

  printf STDERR "r=%d, c=%d, xp=%d, yp=%d\n", $rows//0, $cols//0, 
                                              $xpix//0, $ypix//0;
  $need_update = undef;
  ($maxcols, $maxrows) = ($cols ? $cols : -1, $rows ? $rows : -1);
}

#main

my ($rows,$cols) = getwinsize;

print "rows=$rows, cols=$cols\n";

[download]
But this doesn't work -- returns all zeros for the sizes.

Why? The ioctl works in 'C', why not in Perl?

Thanks!

In reply to Failing to get current TTY's rows & columns... by perl-diddler

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