Simple script for building a changelog since the last tag

changelog.sh

#!/bin/bash
#
# Author: Tyler Stroud <tyler@tylerstroud.com>
# Date: 2017-10-25
#
# This script will build a changelog containing commit messages for all commits since the most recent tag.
# It will prepend a new entry using today's date and the specified tagname followed by the commit messages
# to CHANGELOG.md
#
# Usage: 
# $ ./changelog.sh v1.2.3-the-new-tag-i-am-preparing-to-create

if [ -z "$1" ]; then
    echo -e "You must specify a tag name. This should be the name of the tag you are about to create."
    echo -e "Usage:\n  $0 tagname"
    exit 1;
fi
TAG=$1
DATE=`date +%Y-%m-%d`
CHANGELOG=$(git log `git describe --tags --abbrev=0 HEAD^`..HEAD --pretty="* %s")
TEMPFILE=$(mktemp /tmp/changelog.XXXXXXXX)

tee $TEMPFILE <<EOF 

### $TAG ($DATE)

$CHANGELOG

EOF

# Comment these 2 lines if you do not wish to actually modify your CHANGELOG.md file.
/bin/cat CHANGELOG.md >> $TEMPFILE
/bin/mv $TEMPFILE CHANGELOG.md