aocdl is a command line utility that automatically downloads your Advent of Code puzzle inputs.

This tool is for competitive programmers, who want to solve the puzzles as fast as possible. Using the -wait flag you can actually start the program before the puzzle is published, thus spending exactly zero seconds of competition time on downloading the input (see Basic Usage for details).

If you are working with the command line, it might also be more comfortable to type aocdl -year 2015 -day 1 instead of downloading the puzzle input using the browser.

Trivia: If the puzzle input is very short, it will be embedded into the puzzle page instead of being linked (for an example see day 4 of 2015). Thanks to the consistent API of the Advent of Code website, these puzzle inputs can be downloaded exactly like the normal, longer puzzle inputs.

You can download pre-compiled binaries from the releases page. Just unzip the archive and place the binary in your working directory or in a convenient location in your PATH.

If you have the Go compiler installed, you can use the standard go get command to download, build and install aocdl.

go get -u github.com/GreenLightning/advent-of-code-downloader/aocdl

Your session cookie is required to download your personalized puzzle input. See the two sections below, if you want to know what a session cookie is or how to get yours. The session cookies from the Advent of Code website are valid for about a month, so you only have to get your cookie once per event. You can provide it to aocdl in two ways.

Set your session cookie as a command line parameter:

aocdl -session-cookie 0123456789...abcdef

Or create a configuration file named .aocdlconfig in your home directory or in the current directory and add the session-cookie key:

{
	"session-cookie": "0123456789...abcdef"
}

You can test your setup by downloading an old puzzle input using aocdl -year 2020 -day 1. You will get an appropriate error message if the program cannot find a session cookie. However, if you get a 500 Internal Server Error, this most likely means your session cookie is invalid or expired.

A session cookie is a small piece of data used to authenticate yourself to the Advent of Code web servers. It is not human-readable and might look something like this (this is not a valid cookie):

53616c7465645f5fbd2d445187c5dc5463efb7020021c273c3d604b5946f9e87e2dc30b649f9b2235e8cd57632e415cb

When you log in, the Advent of Code server generates a new session cookie and sends it to your browser, which saves it on your computer. Every time you make a request, your browser sends the cookie back to the server, which is how the server knows that the request is from you and not somebody else. That way the server can send you a personalized version of the website (for example displaying your username and current number of stars or sending you your personal puzzle input instead of somebody else's input).

Google Chrome:

• Go to adventofcode.com
• Make sure you are logged in
• Right click and select "Inspect"
• Select the "Application" tab
• In the tree on the left, select "Storage" → "Cookies" → "https://adventofcode.com"
• You should see a table of cookies, find the row with "session" as name
• Double click the row in the "Value" column to select the value of the cookie
• Press CTRL + C or right click and select "Copy" to copy the cookie
• Paste it into your configuration file or on the command line

Mozilla Firefox:

• Go to adventofcode.com
• Make sure you are logged in
• Right click and select "Inspect Element"
• Select the "Storage" tab
• In the tree on the left, select "Cookies" → "https://adventofcode.com"
• You should see a table of cookies, find the row with "session" as name
• Double click the row in the "Value" column to select the value of the cookie
• Press CTRL + C or right click and select "Copy" to copy the cookie
• Paste it into your configuration file or on the command line

Assuming you have created a configuration file (if not you must provide your session cookie as a parameter), the following command will attempt to download the input for the current day and save it to a file named input.txt:

aocdl

If you specify the -wait flag, the program will display a countdown waiting for midnight (when new puzzles are released) and then download the input of the new day:

aocdl -wait

Finally, you can also specify a day (and year) explicitly.

aocdl -day 1
aocdl -year 2015 -day 1

-session-cookie 0123456789...abcdef
	Use the specified string as session cookie.

-output input.txt
	Save the downloaded puzzle input to the specified file. The special
	markers {{.Year}} and {{.Day}} will be replaced with the selected year
	and day. [see also Go documentation for text/template]

-year 2000
-day 24
	Download the input from the specified year or day. By default the
	current year and day is used.

-force
	Overwrite file if it already exists.

-wait
	If this flag is specified, year and day are ignored and the program
	waits until midnight (when new puzzles are released) and then downloads
	the input of the new day. While waiting a countdown is displayed. To
	reduce load on the Advent of Code servers, the download is started after
	a random delay between 2 and 30 seconds after midnight.

The program looks for configuration files named .aocdlconfig in the user's home directory and in the current working directory.

For each option, the configuration file in the current directory overwrites the configuration file in the home directory and command line parameters overwrite any configuration file.

Configuration files must contain one valid JSON object. The following keys corresponding to some of the command line parameters above are accepted:

A fully customized configuration file might look like this, although the program would only ever download the same input unless the date is specified on the command line:

{
	"session-cookie": "0123456789...abcdef",
	"output": "input-{{.Year}}-{{.Day}}.txt",
	"year": 2015,
	"day": 24
}