#!/usr/local/bin/perl -w
use strict;
use Fcntl;

print "Enter some text to lose...\n";
sleep 4;
print "Losing...\n";
fcntl(STDIN, F_SETFL, O_NONBLOCK)
  or die "Couldn't set STDIN to non-blocking I/O: $!\n";
my $buf;
1 while (sysread(STDIN, $buf, 4096));
print "Reading...\n";

fcntl(STDIN, F_SETFL, 0)
  or die "Couldn't set STDIN to blocking I/O: $!\n";

print scalar <STDIN>;
[download]

The code sleeps for 4 seconds, to let you type in some text. Then it loses that text, and reads in a line.

You might also need something more: the above code deals with whole lines, so any incomplete lines typed before the 4 seconds are up will be kept. To get rid of those, try this (on UNIX):

#!/usr/local/bin/perl -w
use strict;
use Fcntl;

print "Enter some text to lose...\n";
sleep 4;
print "Losing...\n";
system("/bin/stty raw");
die "stty failed\n" if $?;
fcntl(STDIN, F_SETFL, O_NONBLOCK)
  or die "Couldn't set STDIN to non-blocking I/O: $!\n";
my $buf;
print $buf while (sysread(STDIN, $buf, 4096));
print "Reading...\n";

system("/bin/stty cooked");
die "stty failed\n" if $?;
fcntl(STDIN, F_SETFL, 0)
  or die "Couldn't set STDIN to blocking I/O: $!\n";

print scalar <STDIN>;
[download]

Have "fun" (for the UN*Xish definition of "fun")...