git-memo

git-memo.sh

#!/bin/bash
set -e

# Memoizes a functionally pure command using git notes.
#
# Example:
#
#     $ echo 'hello word' | git memo tr 'a-z' 'n-za-m'
#     uryyb jbeq

# TODO set USAGE and LONG_USAGE

# TODO support for argv_0 versioning: if the first command arg is a tracked
#      file under the current git repo, then use its sha in place of command
#      name to compute $memo_id
# TODO support an option for "use this pre-existing git input object"
# TODO support an option for "use this input file path"
# TODO ... either of which could be a tree/directory
# TODO ... which could be supported through more command calling conventions:
# TODO ... pass-a-zip on stdin ( ala git-archive )
# TODO ... expect-a-zip on stdout
# TODO ... expect-a-git-sha on stdout ( git-aware command )
# TODO ... run-within-dir after preparing it
# TODO ... and then take that, or some other $specified output directory

SUBDIRECTORY_OK=1

. "$(git --exec-path)/git-sh-setup"

# soak input into git, computing its hash key
INPUT=$(git hash-object -w --stdin)

# determine the memo note ref for the given command
memo_id=$(echo "$@" | git hash-object -w --stdin)
memo_ref="memo/$memo_id"

# get prior cached output hash key, or run the command and soak its output
if ! OUTPUT=$(git notes --ref "$memo_ref" show "$INPUT" 2>/dev/null); then
    OUTPUT=$(git cat-file blob "$INPUT" | "$@" | git hash-object -w --stdin)
    git notes --ref "$memo_ref" add -f -m "$OUTPUT" "$INPUT" 2>/dev/null
fi

# either way, now you get output
git cat-file blob "$OUTPUT"

NOTE: the .sh extension is just here to hint github as to the language ; in practice, drop the extension when putting it in a bin-dir

Inspired by https://gist.github.com/kriskowal/8bff7993712c328d945710800da8c42c