This repository contains solutions to the 2021 Advent of Code written in the “little languages” of UNIX.

The solutions run directly from source and are intended to conform to the POSIX.1-2017 standard.

Languages Used

• sh - shell, the standard command language interpreter
• awk - pattern scanning and processing language
• bc - arbitrary-precision arithmetic language
• sed - stream editor

Solutions

Day 1	Day 2	Day 3	Day 4	Day 5
Day 6	Day 7	Day 8	Day 9	Day 10
Day 11	Day 12	Day 13	Day 14	Day 15
Day 16	Day 17	Day 18	Day 19	Day 20
Day 21	Day 22	Day 23	Day 24	Day 25

Structure

Each solution consists of a main executable file named solve, and optionally additional source files, in a subdirectory of src/ corresponding to the day and problem. The solve program makes the following assumptions about its environment:

• The TMPDIR environment variable will be set to the path of a writable temporary directory.
• The current working directory will be set to the parent directory of the solve program.
• The program will read the day’s input from stdin.
• The program will write its solution to stdout and exit with a status of zero.

Advent Harness

The repository includes a built-in harness with scripts to fetch advent problem input, record verified output, and stub, run, and test each day’s solutions.

To evaluate a particular solution, run bin/aoc solve <day> <problem>, where <day> is the advent day number and <problem> is 1 or 2.

To test each solution against the recorded output, run bin/aoc test.

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© 2021 Sam Stephenson