#!/bin/sh
set -f

sed -znE '/^([^=]+)=.*$/s,,\1,p' /proc/self/environ \
| sed -zE \
    -e '/^_$/d;/^ENVSUBST_/d;' \
    -e '/^__IEP/d;/^IEP_(INIT|VERBOSE|TRACE)$/d' \
| {
	if [ -n "${ENVSUBST_EXCLUDE_REGEX:-}" ] ; then
		grep -zEv -e "${ENVSUBST_EXCLUDE_REGEX}"
	else
		if [ -n "${ENVSUBST_INCLUDE_REGEX:-}" ] ; then
			grep -zE -e "${ENVSUBST_INCLUDE_REGEX}"
		else
			cat
		fi
	fi
} \
| sort -zV \
| xargs -0 -r printf '${%s} ' \
| sed -zE 's/ $//'