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User Interfaces
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15.8. Using POSIX termios

Problem

You'd like to manipulate your terminal characteristics directly.

Solution

Use the POSIX termios interface.

Description

Think of everything you can do with the stty command  - you can set everything from special characters to flow control and carriage-return mapping. The standard POSIX module provides direct access to the low-level terminal interface to implement stty-like capabilities in your program.

Example 15.2 finds what your tty's erase and kill characters are (probably backspace and Ctrl-U). Then it sets them back to their original values out of antiquity, # and @, and has you type something. It restores them when done.

Example 15.2: demo POSIX termios

#!/usr/bin/perl -w
# demo POSIX termios

use POSIX qw(:termios_h);

$term = POSIX::Termios->new;
$term->getattr(fileno(STDIN));

$erase = $term->getcc(VERASE);
$kill = $term->getcc(VKILL);
printf "Erase is character %d, %s\n", $erase, uncontrol(chr($erase));
printf "Kill is character %d, %s\n", $kill, uncontrol(chr($kill));

$term->setcc(VERASE, ord('#'));
$term->setcc(VKILL, ord('@'));
$term->setattr(1, TCSANOW);

print("erase is #, kill is @; type something: ");
$line = <STDIN>;
print "You typed: $line";

$term->setcc(VERASE, $erase);
$term->setcc(VKILL, $kill);
$term->setattr(1, TCSANOW);

sub uncontrol {
    local $_ = shift;
    s/([\200-\377])/sprintf("M-%c",ord($1) & 0177)/eg;
    s/([\0-\37\177])/sprintf("^%c",ord($1) ^ 0100)/eg;
    return $_;
} 

Here's a module called HotKey that implements a readkey function in pure Perl. It doesn't provide any benefit over Term::ReadKey, but it shows POSIX termios in action:

# 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;

See Also

POSIX Programmer's Guide, by Donald Lewine; O'Reilly & Associates (1991); the documentation for the standard POSIX module, also in Chapter 7 of Programming Perl; Recipe 15.6; Recipe 15.9


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