This script ensures that a command is run only if it hasn't been run before with given arguments, set of dependent files, and specified input values. It uses a hash of the command, arguments, input values, and dependent files to determine if the command needs to be run. Only successful executions are cached. This is useful for long running commands

idempotently

#!/bin/bash

# This script ensures that a command is run only if it hasn't been run before with given arguments, set of dependent files,
# and specified input values.
# It uses a hash of the command, arguments, input values, and dependent files to determine if the command needs to be run.
# Only successful executions are cached.
# This is useful for running commands that are expensive to run multiple times, such as building a project or running a test suite.
# Usage:
# idempotently <dependent_files> // <input_values> -- <command> <arguments>
# Example:
# idempotently file1.txt file2.txt // input1 input2 -- echo "Hello, World!"

# Implementation notes:
# This script keeps the cache of hashes in the ~/.cache/idempotently directory.
# It creates a hash of the command, arguments, input values, and dependent files.
# If the hash file does not exist, it runs the command and saves the hash file.
# If the hash file exists, it does not run the command.
# The hash file is named after the hash of the command, arguments, input values, and dependent files.
# The hash file contains the sha1sums of dependent files.
# The hash file is only used to determine if the command needs to be run.
CACHE_DIR=~/.cache/idempotently
mkdir -p ${CACHE_DIR}

dependents=""
while [[ $1 != "//" ]]; do
  dependents+="$1 "
  shift
done
shift # remove the "//" argument

inputs=""
while [[ $1 != "--" ]]; do
  inputs+="$1 "
  shift
done
shift # remove the "--" argument
command=${*} # Get the command and arguments

hash=$(echo "${inputs}${dependents}${command}" | sha1sum | awk '{print $1}')
cache_file="${CACHE_DIR}/${hash}"
cached_stdout="${CACHE_DIR}/${hash}.out"
cached_stderr="${CACHE_DIR}/${hash}.err"

# Create a temp file and write the result of sha1sum $dependents to it.
temp_file=$(mktemp)
sha1sum $dependents > "$temp_file"

# Check if this command has been run before
if [[ -f ${cache_file} ]] && cmp -s "$temp_file" "$cache_file"; then
  rm "$temp_file"
  cat "$cached_stdout"
  cat "$cached_stderr" >&2
  exit 0
else
  $command > "$cached_stdout" 2> "$cached_stderr"
  ret=$?
  if test $ret -eq 0; then
    mv "$temp_file" "$cache_file"
    cat "$cached_stdout"
    cat "$cached_stderr" >&2
  else
    rm "$temp_file"
    exit $ret
  fi
fi