I'm not exactly why your script crashed. Was there any data in STDIN? Did you try typing something and hitting enter? It might have just been blocking for data\n The diamond operator is line oriented.
When you say "quite a bit of data" doyou mean input that may have line newlines etc.. like a cat bigfile | perlscript.pl?

If you want to slurp filehandled data into a scalar and not just one line at a time, you should undefine the line separator variable like so.

{
   local $/ = undef; # Temporarily undefine record seperator.
   my $var = <STDIN>; # Read it all in.
} # Block ends so local restores value.
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As far as limits, I don't know of any abitrary ones but I would think it would be determined by your C libraries that perl was compiled with.

-Lee

"To be civilized is to deny one's nature."