If you have a while loop that is spinning and you don't want to prompt the user for any key to be pressed such as with <STDIN> but to silently break out when she hits ENTER key use the following 3 line function called "keystroke()" where $j variable will change from 0 to 1 when the ENTER key is pressed:
while (true) {
...
if (&keystroke == 1) {
last;
}
...
}
sub keystroke {
$i = '';
vec($i, fileno(STDIN), 1) = 1;
$j = select ($i, undef, undef, 0);
}