Sed from line 6 on from all txt files and being able to output all the results in a single file

Question

I need to sed from all *.txt files from line 6 until the end All the results should be in a new single file with the name of each file preceding the results

Example: Having different txt files the result should be one single that looks like this taking from the 3rd line to the end

file 1
3
4
5
file 2
3
4
5
file 3
3
4
5

Answer 1

With GNU sed:

sed -s '1F;6,$!d' -- *.txt > output

Portably, you could use awk instead:

awk 'FNR == 1 {print FILENAME}; FNR>=6' ./*.txt > output

(note that in both cases, hidden files are excluded).

Empty files won't be referenced, but files that have fewer than 6 lines will. If you don't want to hear about those, you can do:

sed -s '6F;6,$!d' -- *.txt > output
awk 'FNR == 6 {print FILENAME}; FNR>=6' ./*.txt > output

Or if you want to see all files:

for f in *.txt; do
  printf '%s\n' "$f"
  tail -n +6 < "$f"
done > output

With GNU tail, you also do:

$ tail -vn +6 -- *.txt
==> a.txt <==
6
7
8
9
10

==> b.txt <==
6
7
8
9
10