feat: add script to ease conversion from template to real formula

bin/convert-formula.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env sh
+set -o nounset # Treat unset variables as an error and immediately exit
+set -o errexit # If a command fails exit the whole script
+
+if [ "${DEBUG:-false}" = "true" ]; then
+  set -x # Run the entire script in debug mode
+fi
+
+usage() {
+  echo "usage: $(basename "$0") <new-formula-name>" 1>&2
+  echo 1>&2
+  echo "Convert template-formula to <new-formula-name>-formula." 1>&2
+  echo "<new-formula-name> should be a string of lowercase characters and numbers only." 1>&2
+  echo "<new-formula-name> should not be any of 'bin' 'docs' 'test'." 1>&2
+}
+
+args() {
+  if [ $# -ne 1 ]; then
+    usage
+    exit 1
+  fi
+  NEW_NAME=$1
+  if echo "$NEW_NAME" | grep -E --quiet --invert-match '^[a-z0-9]+$'; then
+    usage
+    exit 1
+  fi
+  if echo bin docs test | grep --quiet --word-regexp "$NEW_NAME"; then
+    usage
+    exit 1
+  fi
+}
+
+convert_formula() {
+  # Empty history and make commit message `semantic-release`-compliant
+  # Works for forks of `template-formula` as well as GitHub "Use this template"
+  git reset \
+    "$(echo 'feat: initial commit' \
+      | git commit-tree 'HEAD^{tree}')"
+  git rm --quiet bin/convert-formula.sh AUTHORS.md CHANGELOG.md
+  git mv template__  "${NEW_NAME}"
+  grep --recursive --files-with-matches --exclude-dir=.git template__ . \
+    | xargs -L 1 ex -sc '%s/template__/'"${NEW_NAME}"'/g|x'
+  # shellcheck disable=SC2016 # Expressions don't expand in single quotes
+  git commit --quiet --all \
+    --message 'feat: convert `template-formula` to `'"${NEW_NAME}"'-formula`
+
+BREAKING CHANGE: changed all state names and ids'
+}
+
+args "$@"
+convert_formula