From perlfaq8:

How do I get the screen size?

If you have Term::ReadKey module installed from CPAN, you can use it to fetch the width and height in characters and in pixels:

  use Term::ReadKey;
  ($wchar, $hchar, $wpixels, $hpixels) = GetTerminalSize();
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This is more portable than the raw "ioctl", but not as illustrative:

  require 'sys/ioctl.ph';
  die "no TIOCGWINSZ " unless defined &TIOCGWINSZ;
  open(TTY, "+</dev/tty") or die "No tty: $!";
  unless (ioctl(TTY, &TIOCGWINSZ, $winsize='')) {
      die sprintf "$0: ioctl TIOCGWINSZ (%08x: $!)\n", &TIOCGWINSZ;
    }
  ($row, $col, $xpixel, $ypixel) = unpack('S4', $winsize);
  print "(row,col) = ($row,$col)";
  print "  (xpixel,ypixel) = ($xpixel,$ypixel)" if $xpixel || $ypixel;
  print "\n";
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End FAQ Entry

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You can also use Curses.pm, check out the LINES and COLS variables.