unix - head AND tail of file

First 10 lines of file.ext, then its last 10 lines:

cat file.ext | head -10 && cat file.ext | tail -10

Last 10 lines of the file, then the first 10:

cat file.ext | tail -10 && cat file.ext | head -10

You can then pipe the output elsewhere too:

(cat file.ext | head -10 && cat file.ext | tail -10 ) | your_program