Detect latest version tag and create a new version based on that and commit type. Only work for "major.minor.patch" format.

versionTag.sh

#!/bin/bash

# get current tag
curr=`git describe --tags --abbrev=0` || curr=""
newTag=""

# check if tag exists
if [ -n "$curr" ]
then
  # got latest tag
  # check tag format
  if [[ $curr =~ [0-9]\.[0-9]\.[0-9] ]]
  then 
    # valid version tag
    IFS=. read major minor patch <<< "$curr"
 
    echo "Current version: $curr"
    echo " Major: $major"
    echo " Minor: $minor"
    echo " Patch: $patch"
    
    action="$1"
    msg="$2"
    echo "major minor patch" | tr " " "\n" | grep -F -q -x "$action" || action=""
    if [ -z "$action" ]
    then
      msg="$1"
      # no argument provided
      echo "Please pick the commit type:"
      select t in "breaking changes" "new features" "bug fixes"; do
        case $t in
          "breaking changes" ) action="major"; break;;
          "new features" ) action="minor"; break;;
          "bug fixes" ) action="patch"; break;;
        esac
      done
    fi
    
    # make the new version
    case $action in
      "major" ) newTag="$(($major + 1)).0.0"; break;;
      "minor" ) newTag="$major.$(($minor + 1)).0"; break;;
      "patch" ) newTag="$major.$minor.$(($patch + 1))"; break;;
    esac
    
    echo "Creating a new $action version: $newTag"
  else
    # invalid version tag
    echo "Invalid version tag: $curr"
  
    # prompt for a valid version
    while true
    do
      read -p "Please input a version with format: 0.0.0 (0.1.0):" newTag
      
      # default to 0.1.0
      if [ -z "$newTag" ]
      then
        newTag="0.1.0"
        break
      fi
    
      # check tag format
      if [[ $newTag =~ [0-9]\.[0-9]\.[0-9] ]]
      then
        break
      fi
    done
  fi
else
  # no tag yet, set initial version
  echo "Please pick initial version:"
  select ver in "0.1.0" "1.0.0"; do
    case $ver in
        "0.1.0" ) newTag="0.1.0"; break;;
        "1.0.0" ) newTag="1.0.0"; break;;
    esac
  done
fi

if [ -z "$msg" ]
then
  read -p "Tag message: (leave blank if not needed)" msg
fi

# final confirm
while true
do
  read -p "Push as version: $newTag? (Y/n)" yn
  case $yn in
    [Yy]*|"" )
      if [ -n "$msg" ]
      then
        git tag -a "$newTag" -m "$msg"
      else
        git tag -a "$newTag"
      fi
      git push origin $newTag
      echo "Done!"
      break;;
    [Nn]* ) exit;;
  esac
done

versionTag2.sh

#!/bin/bash
# with ability to do add commit and push
# may be not that useful though...

# get current tag
curr=`git describe --tags --abbrev=0` || curr=""
newTag=""

# check if tag exists
if [ -n "$curr" ]
then
  # got latest tag
  # check tag format
  if [[ $curr =~ [0-9]\.[0-9]\.[0-9] ]]
  then 
    # valid version tag
    IFS=. read major minor patch <<< "$curr"
 
    echo "Current version: $curr"
    echo " Major: $major"
    echo " Minor: $minor"
    echo " Patch: $patch"
    
    action="$1"
    msg="$2"
    echo "major minor patch" | tr " " "\n" | grep -F -q -x "$action" || action=""
    if [ -z "$action" ]
    then
      msg="$1"
      # no argument provided
      echo "Please pick the commit type:"
      select t in "breaking changes" "new features" "bug fixes"; do
        case $t in
          "breaking changes" ) action="major"; break;;
          "new features" ) action="minor"; break;;
          "bug fixes" ) action="patch"; break;;
        esac
      done
    fi
    
    # make the new version
    case $action in
      "major" ) newTag="$(($major + 1)).0.0"; break;;
      "minor" ) newTag="$major.$(($minor + 1)).0"; break;;
      "patch" ) newTag="$major.$minor.$(($patch + 1))"; break;;
    esac
    
    echo "Creating a new $action version: $newTag"
  else
    # invalid version tag
    echo "Invalid version tag: $curr"
  
    # prompt for a valid version
    while true
    do
      read -p "Please input a version with format: 0.0.0 (0.1.0):" newTag
      
      # default to 0.1.0
      if [ -z "$newTag" ]
      then
        newTag="0.1.0"
        break
      fi
    
      # check tag format
      if [[ $newTag =~ [0-9]\.[0-9]\.[0-9] ]]
      then
        break
      fi
    done
  fi
else
  # no tag yet, set initial version
  echo "Please pick initial version:"
  select ver in "0.1.0" "1.0.0"; do
    case $ver in
        "0.1.0" ) newTag="0.1.0"; break;;
        "1.0.0" ) newTag="1.0.0"; break;;
    esac
  done
fi

# check for uncommitted changes
uncommitted=false
git diff-index --quiet HEAD -- || uncommitted=true
if [ "$uncommitted" = true ]
then
  while true
  do
    read -p "Detected uncommitted changed. Do you want to do commit first? (Y/n)" yn
    case $yn in
      [Yy]*|"" ) 
        # do commit
        # get commit message
        read -p "Commit message: " commitMsg
        if [ -z "$commitMsg" ]
        then
          commitMsg="Commit for version $newTag"
        fi
        
        # confirm before commit
        while true
        do
          read -p "Commit with message: \"$commitMsg\"? (Y/n)" yn
          case $yn in
            [Yy]*|"" )
              git add -A
              git commit -m "$commitMsg"
              break;;
            [Nn]* ) break;;
          esac
        done
        break;;
      [Nn]* ) break;;
    esac
  done  
fi
# check for unpushed commits
commitCount=`git rev-list @{u}..@ --count`
if [ $commitCount -gt 0 ]
then
  # confirm before commit
  while true
  do
    read -p "Push local commits? (Y/n)" yn
    case $yn in
      [Yy]*|"" )
        git push origin HEAD
        echo "Done!"
        git log -n 1
        break;;
      [Nn]* ) break;;
    esac
  done
fi

if [ -z "$msg" ]
then
  read -p "Tag message: (leave blank if not needed)" msg
fi

# final confirm
while true
do
  read -p "Push as version: $newTag? (Y/n)" yn
  case $yn in
    [Yy]*|"" )
      if [ -n "$msg" ]
      then
        git tag -a "$newTag" -m "$msg"
      else
        git tag -a "$newTag"
      fi
      git push origin $newTag
      echo "Done!"
      break;;
    [Nn]* ) exit;;
  esac
done

New to bash, and not expert at git.
Not fully tested.

Any advice or bug report is very welcomed!