gittag-increment.sh

#!/bin/sh

#Get the highest tag number
VERSION=$(git describe --abbrev=0 --tags 2>/dev/null)
VERSION=${VERSION:-'0.0.0'}

#Get number parts
MAJOR="${VERSION%%.*}"; VERSION="${VERSION#*.}"
MINOR="${VERSION%%.*}"; VERSION="${VERSION#*.}"
PATCH="${VERSION%%.*}"; VERSION="${VERSION#*.}"

#Increase version
PATCH=$((PATCH+1))

#Get current hash and see if it already has a tag
GIT_COMMIT=$(git rev-parse HEAD)
NEEDS_TAG=$(git describe --contains "$GIT_COMMIT")

#Create new tag
NEW_TAG="$MAJOR.$MINOR.$PATCH"
echo "Updating to $NEW_TAG"

#Only tag if no tag already (would be better if the git describe command above could have a silent option)
if [ -z "$NEEDS_TAG" ]; then
    echo "Tagged with $NEW_TAG (Ignoring fatal:cannot describe - this means commit is untagged) "
    git tag "$NEW_TAG" -m "autogenerated" -f
else
    echo "Already a tag on this commit"
fi