Display a simple changelog between the last two tags in a Git repository

changelog.sh

#! /usr/bin/env sh

firstTag=$(git tag | sort -r | head -1)
secondTag=$(git tag | sort -r | head -2 | awk '{split($0, tags, "\n")} END {print tags[1]}')
echo "Changes between ${secondTag} and ${firstTag}\n"
git log  --pretty=format:' * %s' ${secondTag}..${firstTag}

Tags sorted by date:

firstTag=$(git tag --sort=-committerdate | head -1)
secondTag=$(git tag --sort=-committerdate | head -2 | tail -1)

Faster (only 1 git command) sorted by date:

latestTags=($(git for-each-ref refs/tags/* --sort=-taggerdate --count=2 --format="%(refname:short)"))
firstTagHF=${latestTags[0]}
secondTagHF=${latestTags[1]}

You can also filter by name if you want:
git for-each-ref refs/tags/<tag_name_start>*