how to extract middle ten lines of a file using linux commands when total number of lines in the file is unknown?

Question

Suppose there is a text file with unknown number of lines and we need to extract ten lines in the middle of the file. How can we achieve the above using Linux commands?

Answer 1

· wc : count lines (first result)

· awk : takes the lines returned by wc, divides by 2 and adds 5

· tail : gets the last -n lines

· head : gets the first -n lines

tail -n `wc filename  | awk '{print (int($1/2)+5) }' `  filename | head -n 10

This is aprox, doesn't work if you need check errors

Answer 2

Use wc to count number of lines

wc -l filename

Then, use Head and Tail to extract lines.
let's assume file has 50 lines.

head -n 30 filename | tail -n +21