my @lines = (
    'a string with numbers and letters 4678',
    '5678',
    '46789',
    ' 4678',
    '4678',
);
open (INPUT, '+<', "tmpfile")    || die $!;
print INPUT $_."\n" for @lines;
seek(INPUT,0,0);
if (my $fh = STDIN->fdopen(\*INPUT, "r")) {
    my $room = enter_number();
    $fh->close;
	print "Room:  $room\n";
}
close INPUT;
unlink 'tmpfile';