Extract middle section of lines of a text file?

If you want not to get messed up but still do it using tail and head, there is a useful way of invoking tail using a line-count from the beginning, not the end:

tail -n +4001 yourfile | head -4000

... But a better, automatic tool made just for splitting files is called... split! It's also a part of GNU coreutils, so any normal Linux system should have it. Here's how you can use it:

split -l 4000 yourInputFile thePrefixForOutputFiles

(See man split if in doubt.)

Combining head and tail as you did will work, but for this I would use sed

sed -n '1,4000p' input_file # print lines 1-4000 of input_file

This lets you solve your problem with a quick shell function

chunk_it(){
    step=4
    start=1
    end=$step
    for n in {1..4} ; do
        sed -n "${start},${end}p" "$1" > "$1".$start-$end
        let start+=$step
        let end+=$step
    done
}

chunk_it your_file

Now you have your_file.1-4000 and yuor_file.4001-8000 and so on.

Note: requires bash