sed with filename from pipe

Question

In a folder I have many files with several parameters in filenames, e.g (just with one parameter) file_a1.0.txt, file_a1.2.txt etc.
These are generated by a c++ code and I'd need to take the last one (in time) generated. I don't know a priori what will be the value of this parameter when the code is terminated. After that I need to copy the 2nd line of this last file.

To copy the 2nd line of the any file, I know that this sed command works:

sed -n 2p filename

I know also how to find the last generated file:

ls -rtl file_a*.txt | tail -1

Question:

how to combine these two operation? Certainly it is possible to pipe the 2nd operation to that sed operation but I dont know how to include filename from pipe as input to that sed command.

Answer 1

You can use this,

ls -rt1 file_a*.txt | tail -1 | xargs sed -n '2p'

(OR)

sed -n '2p' `ls -rt1 file_a*.txt | tail -1`

sed -n '2p' $(ls -rt1 file_a*.txt | tail -1)

Answer 2

Typically you can put a command in back ticks to put its output at a particular point in another command - so

sed -n 2p `ls -rt name*.txt | tail -1 `

Alternatively - and preferred, because it is easier to nest etc -

sed -n 2p $(ls -rt name*.txt | tail -1)