Delete lines X to Y using Mac Unix Sed - macos

Question

Command line on a Mac. Have some text files. Want to remove certain lines from a group of files, then cat the remaining text of the file to a new merged file. Currently have the following attempt:
for file in *.txt;
do echo $file >> tempfile.html;
echo ''>>tempfile.html;
cat $file>>tempfile.html;
find . -type f -name 'tempfile.html' -exec sed -i '' '3,10d' {} +;
find . -type f -name 'tempfile.html' -exec sed -i '' '/<ACROSS>/,$d' {} +;
# ----------------
# some other stuff
# ----------------
done;
I am extracting a section of text from a bunch of files and concating them all together, but still need to know from which file each selection originated. First I concat the name of the file then (supposedly) the selection of text from each file. then repeat the process.
Plus, I need to leave the original text files in place for other purposes.
So the concatinated file would be:
filename1.txt
text-selection
more_text
filename2.txt
even-more-text
text-text-test-test
The first SED is supposed to delete from line 3 to line 10. The second is supposed to delete from the line containing to the end of the file.
However, what happens is the first deletes everything in the tempfile. The second one was doing nothing. (each were tested separately)
What am I doing wrong?
I must be missing something. Even trying -- what appears to be -- a very simple example does not work either. My hope was, the following example, would delete lines 3-10, but save the rest of the file to test.txt.
sed '3,10d' nxd2019-01-06.txt > test.txt

Answer 1

Your invocation of find will attempt to run sed with as many files as possible per call. But note: Addresses in sed do not address lines in each input file, they address the whole input of sed (which can consist out of many input files)
Try this:
> a.txt cat <<EOF
1
2
EOF
> b.txt cat <<EOF
3
4
EOF
Now try this:
sed 1d a.txt b.txt
2
3
4
As you can see, sed removed the first line from a.txt, not from b.txt
The problem in your case, is the second invocation of find. If will remove everything from the first occurrence of ACROSS until the last line in the last file found by find This will effectively remove the content from all but the first tempfile.html.
Having that the remaining logic in your script is working, you should just change the find invocations to:
find . -type f -name 'tempfile.html' -exec sed -i '' '3,10d' {} \;
find . -type f -name 'tempfile.html' -exec sed -i '' '/<ACROSS>/,$d' {} \;
This would call sed once per input file.