A simple way to do what the question asks for, in one command:

awk '{ if (NR <= 1000) print > "piece1"; else print > "piece2"; }' bigfile

or, for those of you who really hate to type long, intuitively comprehensible commands,

awk '{ print > ((NR <= 10000) ? "piece1" : "piece2"); }' bigfile

A simple way to do what the question asks for, in one command:

awk '{ if (NR <= 1000) print > "piece1"; else print > "piece2"; }' bigfile

or, for those of you who really hate to type long, intuitively comprehensible commands,

awk '{ print > ((NR <= 1000) ? "piece1" : "piece2"); }' bigfile