get the second last line from shell pipeline

问题:

I want to get the second last line from the ls -l output. I know that ls -l|tail -n 2| head -n 1 can do this, just wondering if sed can do this in just one command?

回答1:

ls -l|sed -n 'x;$p'

It can't do third to last though, because sed only has 1 hold space, so can only remember one older line. And since it processes the lines one at a time, it does not know the line will be next to last when processing it. awk could return thrid to last, because you can have arbitrary number of variables there, but the script would be much longer than the tail -n X|head -n 1.

回答2:

In a awk one-liner :

echo -e "aaa\nbbb\nccc\nddd" | awk '{v[c++]=$0}END{print v[c-2]}'
ccc

回答3:

Try this to delete second-last line in file

sed -e '$!{h;d;}' -e x filename

回答4:

tac filename | sed -n 2p

-- but involves a pipe, too