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


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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

open(TTY, "+</dev/tty") or die "no tty: $!";
system "stty cbreak </dev/tty >/dev/tty 2>&1";
$key = getc(TTY); # perhaps this works
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;
$key = ReadKey(0);

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();
$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->setcc(VTIME, 0);
$term->setattr($fd_stdin, TCSANOW);

sub readkey {
my $key = '';
sysread(STDIN, $key, 1);
return $key;

END { cooked() }



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