I would like to edit the first and last line in a very huge file (~500GB). How can do so? For example, in the first line I have:
-flag </begin>
and I would like to omit the "-flag". I tried using sed (as shown) to edit the first line but I didn't work:
sed -i '1s/-flag <begin>/<begin>/g' file.txt
I can't think of a way you can do this in-place (I'd be interested to hear one!)
Hardly a one-liner but you could give this a try:
# substitute the first line and exit
sed '1s/-flag \(.*\)/\1/;q' file > new
# add the rest of the file (probably quicker than sed)
tail -n +2 file >> new
# cut off the last line of the file
truncate -s $(( $(stat -c "%s" new) - $(tail -n 1 new | wc -c) )) new
# substitute the last line
tail -n 1 file | sed 's/-flag \(.*\)/\1/' >> new
This assumes you have a couple of tools like truncate and that you can do arithmetic in your shell (my shell is bash).
The truncate -s removes the last line by taking the difference between the total file size stat -c "%s" and the length of the last line in bytes.
I'm not sure what you were trying to remove from the last line but I assumed that it was the same as the first (remove -flag from the start of the line).
Suggested modifications are welcome.