The underscore pseudo-filehandle was described in llama 1 and llama 2, although we've dropped it for llama 3 as being not as important as covering "use strict" a bit better.

The underscore pseudo-filehandle is actually one of the very few features that I can claim is entirely my own idea. I suggested to Larry during the Perl3 alpha testing phase that performing a separate stat operation for each component of -r $foo && -w $foo was wasteful and subject to phase errors. He came up with the underscore cache in response.

The other ideas I can claim directly are the list-slice, and the arrow syntax for dereferencing coderefs (introduced on a bet, but that's another story).

-- Randal L. Schwartz, Perl hacker