#!/usr/bin/env perl

use warnings;
use strict;

use IO::Select;
use IO::Handle;
use Inline 'C';

my $select = IO::Select->new( \*STDIN );
disable_canon_mode() if @ARGV;
# Experiment by commenting out the above line and giving command-line
# arguments.

while ( 1 ) {
    $select->can_read; # block until new input
    warn "CAN_READ STDIN\n";

    my $in;
    if ( @ARGV ) {
        sysread STDIN, $in, 1;
        print "Char read: $in\n";
    }
    else {
        $in = <STDIN>;
        print "Line read: $in\n";
    }
}

__END__
__C__

#include <termios.h>

#define STDIN 0

void disable_canon_mode ()
{
    struct termios tio;

    if ( isatty( STDIN ) == 0 ) { return; }

    /* Turn off canonical mode, meaning read one char at a time.
       Set timer to 0, to wait forever. Minimum chars is 1. */

    tcgetattr( STDIN, &tio );
    tio.c_lflag &= ~ICANON;
    tio.c_cc[ VTIME ] = 0;
    tio.c_cc[ VMIN  ] = 1;
    tcsetattr( STDIN, TCSANOW, &tio );
}