Testing if there is data on stdin?

[Lloyd Zusman <ljz@xxxxxxxxxx>]

Is there a way in zsh to test whether there is at least one byte of data
waiting to be read from stdin without actually reading that data?

I know I can do a [[ -t 0 ]] to see whether stdin is attached to a
terminal, but that doesn't tell me if there is any data waiting to
be read.

The reason I want to do this is because I have a zsh script which, under
certain circumstances, needs to get its arguments via stdin instead of
from the command line. I'd like to be able to test within the script
whether there is data waiting on stdin, and if so, to read it and use it
to construct the argument list. If there is no data waiting on stdin,
then I just want to get the arguments from the command line.

Also, there is a slight difference in processing logic if I find data in
stdin, and I need to do a little bit of special initialization _before_
I try to read that data ... but only if that data is on stdin waiting to
be read.

Any suggestions as to how I might do this? I couldn't find anything in
the zsh docs, but I could easily have overlooked something.

Thanks in advance.


-- 
 Lloyd Zusman
 ljz@xxxxxxxxxx
 God bless you.