treewide: improve template expansion

also: support *.toml as extra configuration dictionaries

scripts/envsubst-single

@@ -0,0 +1,58 @@
+#!/bin/sh
+set -f
+
+src='-' dst='-'
+case $# in
+0 ) ;;
+1 )
+	src="$1"
+	case "$1" in
+	*.in ) dst="${1%".in"}" ;;
+	esac
+;;
+2 ) src="$1" ; dst="$2" ;;
+* ) exit 1 ;;
+esac
+[ -n "${src}" ] || exit 1
+[ -n "${dst}" ] || exit 1
+if [ "${src}" = '-' ] ; then src=/dev/stdin ; fi
+if [ "${dst}" = '-' ] ; then dst=/dev/stdout ; fi
+
+is_same_file() {
+	find -L "$1" -samefile "$2" -printf . -quit 2>/dev/null | grep -Fq . || return 1
+}
+
+if is_same_file "${src}" /dev/stdin ; then src=/dev/stdin ; fi
+if is_same_file "${dst}" /dev/stdout ; then dst=/dev/stdout ; fi
+
+while : ; do
+	if [ "${src}" = '/dev/stdin' ] && [ "${dst}" = '/dev/stdout' ] ; then
+		break
+	fi
+
+	if is_same_file "${src}" "${dst}" ; then
+		exit 1
+	fi
+break ; done
+
+set +e ; unset __ret
+while [ -n "${ENVSUBST_ARGS}" ] ; do
+	[ -f "${ENVSUBST_ARGS}" ] || break
+	[ -s "${ENVSUBST_ARGS}" ] || break
+
+	envsubst "$(cat "${ENVSUBST_ARGS}" </dev/null)" < "${src}" > "${dst}"
+	__ret=$?
+break ; done
+if [ -z "${__ret}" ] ; then
+	envsubst "$(envsubst-args.sh </dev/null)" < "${src}" > "${dst}"
+	__ret=$?
+fi
+
+while : ; do
+	[ "${ENVSUBST_UNLINK_SRC}" = 1 ] || break
+	[ "${src}" != '/dev/stdin' ] || break
+
+	rm -f "${src}"
+break ; done
+
+exit ${__ret}