How to use sed to remove the last n lines of a fil

Question

I want to remove some n lines from the end of a file. Can this be done using sed?

For example, to remove lines from 2 to 4, I can use

$ sed '2,4d' file

But I don't know the line numbers. I can delete the last line using

$sed $d file

but I want to know the way to remove n lines from the end. Please let me know how to do that using sed or some other method.

Answer 1

To delete last 4 lines:

$ nl -b a file | sort -k1,1nr | sed '1, 4 d' | sort -k1,1n | sed 's/^ *[0-9]*\t//'   

Answer 2

A funny & simple sed and tac solution :

n=4
tac file.txt | sed "1,$n{d}" | tac

NOTE

• double quotes " are needed for the shell to evaluate the $n variable in sed command. In single quotes, no interpolate will be performed.
• tac is a cat reversed, see man 1 tac
• the {} in sed are there to separate $n & d (if not, the shell try to interpolate non existent $nd variable)