version improvements

scripts_version

#!/bin/sh -e
#
# Checked environment variables:
# - PLOWSHARE_FORCE_VERSION
# - SOURCE_DATE_EPOCH (see reproducible-builds.org)
#
# Note:
# Choose "git describe" revision syntax: v1.0.1-17-g390e0fa
# over usual (distro) one: 1.0.1~git20140411-390e0fa

if [ $# -ne 0 ]; then
  echo 'warning: this script does not take any argument.' >&2
fi

datefmt='%Y-%m-%d'
if [ -n "$SOURCE_DATE_EPOCH" ]; then
  if date --version 2>/dev/null | head -n1 | grep -q GNU; then
    date=$(date -u -d "@$SOURCE_DATE_EPOCH" +$datefmt)
  else
    date=$(date -u -r "$SOURCE_DATE_EPOCH" +$datefmt)
  fi
else
  date=$(date -u +$datefmt)
fi

# Check environment variable PLOWSHARE_FORCE_VERSION
# For example: "1.0.1"
if [ -n "$PLOWSHARE_FORCE_VERSION" ]; then
  echo "v${PLOWSHARE_FORCE_VERSION#v} ($date)"
elif git rev-parse --is-inside-work-tree 1>/dev/null 2>&1; then
  rev=$(git describe --always --tags)
  date=$(git log "$rev" -n1 --pretty=%ci | cut -d' ' -f1)
  echo "$rev ($date)"
else
  # Check directory name. For example: plowshare-2.1.7
  dir=$(basename "$PWD")
  v=${dir##*-}
  if echo $v | grep -q '[2-9]\(\.[0-9]\)\{2\}'; then
    echo "v$v ($date)"
  else
    echo 'warning: unable to detect plowshare version.' >&2
    echo "UNKNOWN ($date)"
  fi
fi