Script that will find the last Git Tag and increment it. It will only increment when the latest commit does not already have a tag. By default it increments the patch number, you can tell it to change the major or minor versions by adding #major or #minor to the commit message.

auto-increment-version.sh

#!/bin/bash

#get highest tag number
VERSION=`git describe --abbrev=0 --tags`

#replace . with space so can split into an array
VERSION_BITS=(${VERSION//./ })

#get number parts and increase last one by 1
VNUM1=${VERSION_BITS[0]}
VNUM2=${VERSION_BITS[1]}
VNUM3=${VERSION_BITS[2]}
VNUM1=`echo $VNUM1 | sed 's/v//'`

# Check for #major or #minor in commit message and increment the relevant version number
MAJOR=`git log --format=%B -n 1 HEAD | grep '#major'`
MINOR=`git log --format=%B -n 1 HEAD | grep '#minor'`

if [ "$MAJOR" ]; then
    echo "Update major version"
    VNUM1=$((VNUM1+1))
    VNUM2=0
    VNUM3=0
elif [ "$MINOR" ]; then
    echo "Update minor version"
    VNUM2=$((VNUM2+1))
    VNUM3=0
else
    echo "Update patch version"
    VNUM3=$((VNUM3+1))
fi


#create new tag
NEW_TAG="v$VNUM1.$VNUM2.$VNUM3"

echo "Updating $VERSION to $NEW_TAG"

#get current hash and see if it already has a tag
GIT_COMMIT=`git rev-parse HEAD`
NEEDS_TAG=`git describe --contains $GIT_COMMIT`

#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
    git push --tags
else
    echo "Already a tag on this commit"
fi

Thanks for sharing!

This one checks if previous tags already contain a v , if not it it won't include a v in the next tag

#!/bin/sh

#get highest tag number
VERSION=`git describe --abbrev=0 --tags`
V=""
if [[ $VERSION =~ "v" ]]; then
    V="v"
fi
#get number parts and increase last one by 1
VNUM1=$(echo "$VERSION" | cut -d"." -f1)
VNUM2=$(echo "$VERSION" | cut -d"." -f2)
VNUM3=$(echo "$VERSION" | cut -d"." -f3)
VNUM1=`echo $VNUM1 | sed 's/v//'`

# Check for #major or #minor in commit message and increment the relevant version number
MAJOR=`git log --format=%B -n 1 HEAD | grep '#major'`
MINOR=`git log --format=%B -n 1 HEAD | grep '#minor'`

if [ "$MAJOR" ]; then
    echo "Update major version"
    VNUM1=$((VNUM1+1))
    VNUM2=0
    VNUM3=0
elif [ "$MINOR" ]; then
    echo "Update minor version"
    VNUM2=$((VNUM2+1))
    VNUM3=0
else
    echo "Update patch version"
    VNUM3=$((VNUM3+1))
fi


#create new tag
NEW_TAG="$V$VNUM1.$VNUM2.$VNUM3"

if [ $NEW_TAG = "..1" ]; then
    NEW_TAG="v0.0.1"
fi

echo "Updating $VERSION to $NEW_TAG"

#get current hash and see if it already has a tag
GIT_COMMIT=`git rev-parse HEAD`
NEEDS_TAG=`git describe --contains $GIT_COMMIT 2>/dev/null`

#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
    git push --tags
else
    echo "Already a tag on this commit"
fi

I just added --match="v[0-9]*" to the first line.
It allows to filter tags and have only v[n] tags listed

VERSION=`git describe --abbrev=0 --tags --match="v[0-9]*"`