commit 5c6a17174f6675d01bf35999b025c0e99297a844
parent a4d6defa1722d52bf0f5bb2f3abf1443c4b6509c
Author: Sebastiano Tronto <sebastiano@tronto.net>
Date: Sat, 29 Nov 2025 14:52:27 +0100
Blog post
Diffstat:
2 files changed, 88 insertions(+), 0 deletions(-)
diff --git a/src/blog/2025-11-29-aoc-download/aoc-download.md b/src/blog/2025-11-29-aoc-download/aoc-download.md
@@ -0,0 +1,88 @@
+# Downloading AoC puzzle inputs with curl
+
+As in the [past couple of years](../2023-12-25-advent-of-code), soon
+I am going to take part in the daily programming challenges of the
+[Advent of Code](https://adventofcode.com). This time I decided to take
+some time and optimize my working setup a little bit - not that it matters
+for someone solving the problems at my speed.
+
+So let me show you how I automated downloading the inputs for the puzzles
+(which require you to login) using [curl](https://curl.se).
+
+## The problem
+
+In case you are not familiar with the Advent of Code, it is a casual
+programming challenge that takes place every year in December. Every day
+a new problem is released, and you are supposed to write a program that
+solves it and submit your answer as a short string, usually a number.
+The fastest you solve the problems, the more internet points
+you get, and you can brag about it with your colleagues.
+
+The input data for each problem is given as a simple text file. Not
+everyone gets the same, there are a few (hundreds? thousands? not sure)
+of different inputs, and each user is assigned one.
+
+This means that one must log in to be able to download their puzzle input.
+To manually download the input file is quite tedious, so it would be nice
+if there was a way to automate this. Of course,
+[I am](https://github.polettix.it/ETOOBUSY/2022/11/28/aoc-inputs-downloader)
+[not](https://packagist.org/packages/colinodell/aoc-downloader)
+[the](https://github.com/johlinco/aoc-cli)
+[first](https://github.com/Gronner/aoc-downloader)
+[to](https://github.com/czyber/aoc-downloader)
+[think](https://github.com/martintc/aoc-downloader-rs)
+[about](https://github.com/scarvalhojr/aoc-cli)
+[doing](https://github.com/colinodell/aoc-downloader)
+[this](https://github.com/GreenLightning/advent-of-code-downloader).
+
+## Session cookies
+
+If log in was not required, we could simply download the input file for,
+say, day 12 of 2024 and save it to `input.txt` with curl like this:
+
+```
+$ curl https://adventofcode.com/2024/day/12/input -o input.txt
+```
+
+But if you run this command, you'll get something like this:
+
+```
+Puzzle inputs differ by user. Please log in to get your puzzle input.
+```
+
+To make curl act as if we were logged in, we need a
+[session cookie](https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/Cookies).
+If you log into [adventofcode.com](https://adventofcode.com) on a browser such
+as Firefox, you can right-click on the page, select "Inspect" and then navigate
+to Storage and then Cookies.
+
+
+
+The long alphanumerical string under "Value" is your session cookie. Anyone
+who gets a hold of it can pretend to be you on this website - by the way,
+this is how the famous YouTube channel
+[Linus tech tips got hacked](https://www.youtube.com/watch?v=yGXaAWbzl5A)
+a couple of years ago.
+
+Save this cookie somewhere, for example in an
+[environment variable](https://en.wikipedia.org/wiki/Environment_variable)
+called `AOC_SESSION_COOKIE`. Then run your curl with an extra option, like so:
+
+```
+$ curl https://adventofcode.com/2024/day/12/input -H "cookie: session=$AOC_SESSION_COOKIE" -o input.txt
+```
+
+And you are good to go!
+
+## The fancy script
+
+Typing out the full command above may look cooler than downloading the file
+by right-clicking "Save page as", but it is just as annoying. So obviously I
+saved that command to
+[a script](https://git.tronto.net/scripts/file/aoc.html)
+that also detects the correct file to download based on the current date
+(or on two optional parameters for the year and the day). My script also
+opens up an editor and [Lynx](https://en.wikipedia.org/wiki/Lynx_(web_browser))
+session to set me up to speed, but that is not as interesting.
+
+Happy coding!
diff --git a/src/blog/2025-11-29-aoc-download/cookie.png b/src/blog/2025-11-29-aoc-download/cookie.png
Binary files differ.
