Automatically bump Git tag versions and create a new tag

release.sh

#!/bin/sh

# BSD 3-Clause License
# 
# Copyright (c) 2017, Péter Szakszon
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# Source of this script:
# https://gist.github.com/szxp/2b0e5e86c1350274f049a28392fc25e0

# This script is shared on reddit. Don't delete it.
# https://www.reddit.com/r/git/comments/6nlnec/automatically_bump_git_tag_versions_and_create_a/?ref=share&ref_source=link

# A more complete example can be found here:
# https://github.com/szxp/kolibri/blob/master/release.sh

progname="$(basename $0)"
lockdir=/var/tmp/myserice-release
pidfile=$lockdir/pid

usage() {
    cat <<EOM
Usage

    $progname [<newtag> [<commit>]]
    $progname [-h|--help]

Description

    It tries to find the closest reachable tag from the specified commit 
    by git-describe. If <commit> argument is missing it defaults to HEAD. 
    The supported tag format is vX.Y.Z[-any-optional-suffix].

    Before the real tagging the user will be prompted for an 'Are you sure?'
    answer.

Examples

1) Suppose that there isn't any reachable tag by git-describe yet. 
   The suggested new tag will be:

     $progname                 -> v1.0.0
     $progname v1.2.3          -> v1.2.3
     $progname v1.2.3-ce       -> v1.2.3-ce
     $progname v1.2.3 abcd123  -> v1.2.3

2) Suppose that the closest reachable tag by git-describe is v1.2.1. 
   The suggested new tag will be:

     $progname                 -> v1.3.0
     $progname minor           -> v1.3.0
     $progname minor abcd123   -> v1.3.0
     $progname patch           -> v1.2.2
     $progname major           -> v2.0.0
     $progname v1.2.3          -> v1.2.3
     $progname v1.2.3 abcd123  -> v1.2.3
     $progname invalid         -> unsupported tag format
     $progname invalid abcd123 -> unsupported tag format

EOM
    exit 0
}
if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
    usage
fi



clean_up() {
    echo "Clean up"
    trap - INT TERM HUP EXIT
    rm -rf "$lockdir"
    exit $1
}

error() {
    echo "${progname}: ${1:-"unknown error"}" 1>&2
}

error_exit() {
    error "$1"
    clean_up 1
}

git_describe() {
    commitish="${1:-"HEAD"}"
    git describe --always --first-parent "$commitish" || error_exit "cannot describe $commitish"
}

create_tag() {
    tag="$1"
    commit="${2:-"HEAD"}"
    commit="$(git rev-parse --verify --short ${commit}^{commit})"
    [ "$?" -eq 0 ] || error_exit "cannot rev-parse $2"

    newtag=   
    oldtag=
    major=
    minor=
    patch=
    ver="$(git_describe $commit)"
    ver="$(echo "$ver" | grep -oP -e '^v[0-9+\.[0-9]+\.[0-9]+')"
    if [ "$?" -eq 0 ]; then       
        oldtag="$ver"
        ver=${ver#v}
        IFS=. read major minor patch <<EOF
$ver
EOF
    fi
    
    if [ -n "$oldtag" ]; then
        case "$tag" in
            "major") newtag="v$(expr $major + 1).0.0" ;;
            "minor") newtag="v$major.$(expr $minor + 1).0" ;;
            "patch") newtag="v$major.$minor.$(expr $patch + 1)" ;;
        esac
    fi

    if [ -z "$newtag" ] && [ -n "$tag" ]; then
        case "$tag" in
            "major") error_exit "cannot increment major number, because no previous tag can be found" ;;
            "minor") error_exit "cannot increment minor number, because no previous tag can be found" ;;
            "patch") error_exit "cannot increment patch number, because no previous tag can be found" ;;
             v*.*.*) newtag="$tag" ;;
                  *) error_exit "unsupported tag format '$tag'; supported formats: 'major', 'minor', 'patch', 'vX.Y.Z'" ;;
        esac
    fi
    
    if [ -z "$newtag" ]; then
        newtag="v1.0.0"
    fi

    while true; do
        read -p "Reachable previous tag from commit $commit: '${oldtag:-"none"}'. Do you wish to create tag '$newtag'? [y/n] " yn
        case $yn in
            [Yy]*) break ;;
            [Nn]*) error_exit "aborted" ;;
                *) echo "Please answer y[es] or n[o]" ;;
        esac
    done
    
    echo "Create tag $newtag $commit"
    git tag -a "$newtag" -m "version $newtag" "$commit" || error_exit "cannot create tag $newtag"
}

trap clean_up INT TERM HUP EXIT

if ( mkdir ${lockdir} ) 2> /dev/null; then
    echo $$ > $pidfile || error_exit "cannot write $pidfile"
    create_tag "$1" "$2"
else
    error "lock exists: $lockdir owned by $(cat $pidfile)"
fi

I'm assuming that gnu grep is likely what you want to be installed?

It would be nice of abcd123 part of each command instead of being ignored could be appended to the version to support pre-releases, release candidates, and build tags:

add another "suffix" arg? such that you can do $prog minor --suffix rc.1

https://semver.org/spec/v2.0.0-rc.1.html#spec-item-12