One liner to format a git tag / branch name appropriately for a docker tag

valid_docker_tag_name

# 1. Replace any non valid characters with dash
# 2. Remove any .- from start of name
# 3. Replace duplicate dash with a single one
# 3. Replace duplicate underscore with a single one
# 4. Replace duplicate dot with a single one
# 5. Truncate string to 128 chars (or less)
sed -e 's/[^[:alnum:]\.\_\-]/-/g' \
    -e 's|^[.-]\+||g' \
    -e 's|-\+|-|g' \
    -e 's|_\+|_|g' \
    -e 's|\.\+|.|g' \
    -e 's/^\(.\{128\}\).*/\1/'