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perlfaq8 - System Interaction ($Revision: 10183 $)
This section of the Perl FAQ covers questions involving operating
system interaction. Topics include interprocess communication (IPC),
control over the user-interface (keyboard, screen and pointing
devices), and most anything else not related to data manipulation.
Read the FAQs and documentation specific to the port of perl to your
operating system (eg, the perlvms manpage, the perlplan9 manpage, ...). These should
contain more detailed information on the vagaries of your perl.
The $^O variable ($OSNAME if you use English) contains an indication of
the name of the operating system (not its release number) that your perl
binary was built for.
Because that's what it does: it replaces your currently running
program with a different one. If you want to keep going (as is
probably the case if you're asking this question) use system()
instead.
How you access/control keyboards, screens, and pointing devices
("mice") is system-dependent. Try the following modules:
- Keyboard
-
Term::Cap Standard perl distribution
Term::ReadKey CPAN
Term::ReadLine::Gnu CPAN
Term::ReadLine::Perl CPAN
Term::Screen CPAN
- Screen
-
Term::Cap Standard perl distribution
Curses CPAN
Term::ANSIColor CPAN
- Mouse
-
Tk CPAN
Some of these specific cases are shown as examples in other answers
in this section of the perlfaq.
In general, you don't, because you don't know whether
the recipient has a color-aware display device. If you
know that they have an ANSI terminal that understands
color, you can use the Term::ANSIColor module from CPAN:
use Term::ANSIColor;
print color("red"), "Stop!\n", color("reset");
print color("green"), "Go!\n", color("reset");
Or like this:
use Term::ANSIColor qw(:constants);
print RED, "Stop!\n", RESET;
print GREEN, "Go!\n", RESET;
Controlling input buffering is a remarkably system-dependent matter.
On many systems, you can just use the stty command as shown in
getc in the perlfunc manpage, but as you see, that's already getting you into
portability snags.
open(TTY, "+</dev/tty") or die "no tty: $!";
system "stty cbreak </dev/tty >/dev/tty 2>&1";
$key = getc(TTY);
sysread(TTY, $key, 1);
system "stty -cbreak </dev/tty >/dev/tty 2>&1";
The Term::ReadKey module from CPAN offers an easy-to-use interface that
should be more efficient than shelling out to stty for each key.
It even includes limited support for Windows.
use Term::ReadKey;
ReadMode('cbreak');
$key = ReadKey(0);
ReadMode('normal');
However, using the code requires that you have a working C compiler
and can use it to build and install a CPAN module. Here's a solution
using the standard POSIX module, which is already on your systems
(assuming your system supports POSIX).
use HotKey;
$key = readkey();
And here's the HotKey module, which hides the somewhat mystifying calls
to manipulate the POSIX termios structures.
package HotKey;
@ISA = qw(Exporter);
@EXPORT = qw(cbreak cooked readkey);
use strict;
use POSIX qw(:termios_h);
my ($term, $oterm, $echo, $noecho, $fd_stdin);
$fd_stdin = fileno(STDIN);
$term = POSIX::Termios->new();
$term->getattr($fd_stdin);
$oterm = $term->getlflag();
$echo = ECHO | ECHOK | ICANON;
$noecho = $oterm & ~$echo;
sub cbreak {
$term->setlflag($noecho);
$term->setcc(VTIME, 1);
$term->setattr($fd_stdin, TCSANOW);
}
sub cooked {
$term->setlflag($oterm);
$term->setcc(VTIME, 0);
$term->setattr($fd_stdin, TCSANOW);
}
sub readkey {
my $key = '';
cbreak();
sysread(STDIN, $key, 1);
cooked();
return $key;
}
END { cooked() }
1;
The easiest way to do this is to read a key in nonblocking mode with the
Term::ReadKey module from CPAN, passing it an argument of -1 to indicate
not to block:
use Term::ReadKey;
ReadMode('cbreak');
if (defined ($char = ReadKey(-1)) ) {
} else {
}
ReadMode('normal');
If you only have do so infrequently, use system:
system("clear");
If you have to do this a lot, save the clear string
so you can print it 100 times without calling a program
100 times:
$clear_string = `clear`;
print $clear_string;
If you're planning on doing other screen manipulations, like cursor
positions, etc, you might wish to use Term::Cap module:
use Term::Cap;
$terminal = Term::Cap->Tgetent( {OSPEED => 9600} );
$clear_string = $terminal->Tputs('cl');
If you have Term::ReadKey module installed from CPAN,
you can use it to fetch the width and height in characters
and in pixels:
use Term::ReadKey;
($wchar, $hchar, $wpixels, $hpixels) = GetTerminalSize();
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";
(This question has nothing to do with the web. See a different
FAQ for that.)
There's an example of this in crypt in the perlfunc manpage). First, you put the
terminal into "no echo" mode, then just read the password normally.
You may do this with an old-style ioctl() function, POSIX terminal
control (see the POSIX manpage or its documentation the Camel Book), or a call
to the stty program, with varying degrees of portability.
You can also do this for most systems using the Term::ReadKey module
from CPAN, which is easier to use and in theory more portable.
use Term::ReadKey;
ReadMode('noecho');
$password = ReadLine(0);
This depends on which operating system your program is running on. In
the case of Unix, the serial ports will be accessible through files in
/dev; on other systems, device names will doubtless differ.
Several problem areas common to all device interaction are the
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