FAQ 8.5 How do I read just one key without waiting for a return key?


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This is an excerpt from the latest version perlfaq8.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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8.5: How do I read just one key without waiting for a return key?

Controlling input buffering is a remarkably system-dependent matter. On
many systems, you can just use the stty command as shown in "getc" in
perlfunc, 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); # perhaps this works
# OR ELSE
sysread(TTY, $key, 1); # probably this does
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 system (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.

# HotKey.pm
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); # ok, so i don't want echo either
$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;



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