Generate markdown changelogs from git tags and the commits between them

git-changelog.sh

#!/bin/sh

set -e

# For each tag in the repository (sorted in reverse chronological order), print
# something like the following:
#
# ## Version <TAG>
# <Tag body, if it has one, but not the body of the pointed-to commit>
#
# ### Included changes
# - abc1234: <commit subject>
# - abc2345: <commit subject>
#
# The commits are listed in chronological order (older commits first). The
# "Included changes" section is not present for the first commit.

git tag --list --sort=-creatordate | while IFS= read -r tag; do
  prev="$(git describe --tags --abbrev=0 "${tag}^" 2>/dev/null)" || true
  printf "## Version %s\n" "$tag"
  git for-each-ref "refs/tags/$tag" \
    --format='%(if:equals=tag)%(objecttype)%(then)%(contents:body)%(end)'
  if [ -n "$prev" ]; then
    printf "### Included changes\n"
    git log "${prev}..${tag}" --reverse --pretty='tformat:- %h: %s'
    printf "\n"
  fi
done