detect input available from command line

[mifflin]

I have a program that may try to get data from the command line using

while (<>) {
}

However, there may not be any input. How do I detect if there is any input so the read will not block? Something like...

if (data is available then) {
    while (<>) {
    }
}
else {
    # do something else
}

UPDATE:

Here is what I ended up doing get the behavior I was looking for...

    my $stdin = IO::Select->new(\*STDIN);
    open my $fh, '|-', $cmd or die $!;
    if (@ARGV || $stdin->can_read(0)) {
        while (<>) {
            print {$fh} $_ or die $!;
        }
    }
    else {
        print {$fh} "\n" or die $!;
    }
    close $fh or die $!;

Now, now matter how the user wants to give my prog the data like...

$ echo "text" | myprog

or

$ myprog <<EOT
some text
EOT

or

$ myprog afile

I get text without blocking.