Add Output The Last N Bytes Of A Large File as a Unix TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1337 TILs and counting..._
+_1338 TILs and counting..._
 
 ---
 
@@ -1318,6 +1318,7 @@ _1337 TILs and counting..._
 - [Occupy A Local Port With Netcat](unix/occupy-a-local-port-with-netcat.md)
 - [Only Show The Matches](unix/only-show-the-matches.md)
 - [Open The Current Command In An Editor](unix/open-the-current-command-in-an-editor.md)
+- [Output The Last N Bytes Of A Large File](unix/output-the-last-n-bytes-of-a-large-file.md)
 - [Partial String Matching In Bash Scripts](unix/partial-string-matching-in-bash-scripts.md)
 - [PID Of The Current Shell](unix/pid-of-the-current-shell.md)
 - [Print A Range Of Lines For A File With Bat](unix/print-a-range-of-lines-for-a-file-with-bat.md)

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

@@ -0,0 +1,32 @@
+# 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:
+
+```bash
+$ tail -c 100 data.json
+```
+
+That didn't quite show me enough info, so I bumped it up:
+
+```bash
+$ 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.