I have a program that may try to get data from the command line using 
while (<>) {
}

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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
}

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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 $!;

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Now, now matter how the user wants to give my prog the data like... 
$ echo "text" | myprog

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or 
$ myprog <<EOT
some text
EOT

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or 
$ myprog afile

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I get text without blocking.

In reply to detect input available from command line by mifflin

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