output-the-last-n-bytes-of-a-large-file.md

Output The Last N Bytes Of A Large File

After creating a massive JSON file as part of a data export, I wanted to check the timestamp of the last value in the file. However, even for Vim, the file was big and it was taking a while to bring the whole thing into memory.

I didn't really need to open it in a full-fledged editor, I just needed to grab the trailing bits (bytes!) of the file until I could see enough data to verify the export.

The tail command is a great tool for this because it can quickly read information from the end of a file. The -c flag in particular allows you to grab the last N bytes of the file and output them.

So, I started with:

$ tail -c 100 data.json

That didn't quite show me enough info, so I bumped it up:

$ tail -c 1000 data.json

That time I was able to see enough to verify the export.

Both commands ran instantaneously, meanwhile my editor was still opening the file.

See man tail for more details.