diff --git a/sh/core/code.sh b/sh/core/code.sh
index 18860ab..a4a5eb0 100644
--- a/sh/core/code.sh
+++ b/sh/core/code.sh
@@ -8,7 +8,7 @@
 
 # TODO variablize
 # path to the entrypoint main file of the project
-RWX_MAIN_PATH="${RWX_ROOT_SYSTEM}/${RWX_MAIN_NAME}.sh"
+RWX_MAIN_PATH="${RWX_ROOT_SYSTEM}/${RWX_MAIN_NAME}.${RWX_MAIN_EXTENSION}"
 # user root directory of the project
 RWX_SELF_USER="${HOME}/${RWX_SELF_NAME}"
 
@@ -59,7 +59,7 @@ rwx_code_install() {
 	fi
 	# commands
 	root="${target}/usr/local/bin"
-	name="${RWX_SELF_NAME}.sh"
+	name="${RWX_SELF_NAME}.${RWX_MAIN_EXTENSION}"
 	file="${root}/${name}"
 	rwx_remove "${file}"
 	rwx_link "${file}" "${RWX_MAIN_PATH}"
@@ -71,7 +71,7 @@ rwx_code_install() {
 ${_rwx_code_commands}
 EOF
 	# sh
-	file="${target}/etc/profile.d/${RWX_SELF_NAME}.sh"
+	file="${target}/etc/profile.d/${RWX_SELF_NAME}.${RWX_MAIN_EXTENSION}"
 	rwx_remove "${file}"
 	rwx_file_write "${file}" "\
 export ENV=\"${RWX_MAIN_PATH}\"
diff --git a/sh/lint/shellcheck.sh b/sh/lint/shellcheck.sh
index 3bdfa07..75101f2 100644
--- a/sh/lint/shellcheck.sh
+++ b/sh/lint/shellcheck.sh
@@ -4,7 +4,7 @@ rwx_shellcheck() {
 	file="$(mktemp)"
 	modules="$(rwx_main_find "${root}")"
 	while IFS= read -r module; do
-		path="${root}/${module}.sh"
+		path="${root}/${module}.${RWX_MAIN_EXTENSION}"
 		echo ". \"${path}\"" >>"${file}"
 	done <<EOF
 ${modules}
diff --git a/sh/main.sh b/sh/main.sh
index ed09edf..401fccd 100755
--- a/sh/main.sh
+++ b/sh/main.sh
@@ -8,6 +8,9 @@
 # │ main │ constants │
 # ╰──────┴───────────╯
 
+# extension of shell modules
+RWX_MAIN_EXTENSION="sh"
+
 # name of the entrypoint module
 RWX_MAIN_NAME="main"
 # name of the project itself
@@ -36,7 +39,7 @@ rwx_main_find() {
 	local root="${1}"
 	find \
 		"${root}" \
-		-name "*.sh" \
+		-name "*.${RWX_MAIN_EXTENSION}" \
 		-type "f" \
 		-printf "%P\n" |
 		sed "s|\\.[^.]*\$||" |
@@ -88,7 +91,7 @@ rwx_main_source() {
 			count=$((count + 1))
 			_rwx_main_log "$(printf "%02d" "${count}") ${module}"
 			# shellcheck disable=SC1090
-			. "${root}/${module}.sh"
+			. "${root}/${module}.${RWX_MAIN_EXTENSION}"
 			# cache code
 			rwx_main_cache "${root}" "${module}"
 		fi
@@ -107,7 +110,7 @@ EOF
 rwx_main_cache() {
 	local root="${1}"
 	local module="${2}"
-	local path="${root}/${module}.sh"
+	local path="${root}/${module}.${RWX_MAIN_EXTENSION}"
 	local text
 	text="$(cat "${path}")"
 	# all source code
diff --git a/sh/self.sh b/sh/self.sh
index 4b25c38..fc62d88 100644
--- a/sh/self.sh
+++ b/sh/self.sh
@@ -11,11 +11,11 @@ rwx_self_subset() {
 	local argument file root
 	for argument in "${@}"; do
 		root="${RWX_ROOT_SYSTEM}/${argument}"
-		file="${argument}.sh"
+		file="${argument}.${RWX_MAIN_EXTENSION}"
 		if [ -d "${root}" ]; then
 			local file
 			for file in $(rwx_main_find "${root}"); do
-				echo "${argument}/${file}.sh"
+				echo "${argument}/${file}.${RWX_MAIN_EXTENSION}"
 			done
 		elif [ -f "${RWX_ROOT_SYSTEM}/${file}" ]; then
 			echo "${file}"