New ENV command for environment variables

ENV can be either used to pass environment variables to be used within
the image or be substituted beforehand. This allows another kind of
variables within a Pifile.

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Added
+- New `ENV` command for environment variables.
 
 ## [0.4.4] - 2021-11-09
 ### Added

README.md

@@ -162,6 +162,22 @@ The optionally permission mode (*chmod*) can be set as the first parameter.
 #### `WORKDIR /my/guest/path`
 `WORKDIR` sets the working directory within the image.
 
+#### `ENV KEY [VALUE]`
+`ENV` either sets or unsets an environment variable to be used within the image.
+If two parameters are given, the first is the key and the second the value.
+If one parameter is given, the environment variable will be removed.
+
+An environment variable can be either used via `$VAR` within another sub-shell (`sh -c 'echo $VAR'`) or substituted beforehand via `@@VAR@@`.
+
+```
+ENV FOO BAR
+
+RUN sh -c 'echo FOO = $FOO'   # FOO = BAR - substituted within a sh in the image
+RUN echo FOO = @@FOO@@        # FOO = BAR - substituted beforehand via pimod
+
+ENV FOO
+```
+
 #### `RUN CMD [PARAMS...]`
 `RUN` executes a command in the chrooted image based on QEMU user emulation.
 

examples/RPi-RaspberryPiOSLite.Pifile

@@ -12,3 +12,13 @@ RUN bash -c "
     echo hello
     echo world
 "
+
+# test environment vars via ENV
+ENV FOO BAR
+RUN sh -c 'echo FOO = $FOO'
+RUN echo FOO = @@FOO@@
+
+# unset FOO again
+ENV FOO
+RUN sh -c 'echo FOO = $FOO'
+RUN echo FOO = @@FOO@@

modules/env.sh

@@ -0,0 +1,44 @@
+# ENV_VARS is an associative array of environment variables, set via ENV.
+declare -A ENV_VARS=()
+
+# env_vars_set saves an environment variable mapping.
+# Usage: env_vars_set KEY VALUE
+env_vars_set() {
+  ENV_VARS["${1}"]="${2}"
+}
+
+# env_vars_del removes an environment variable mapping.
+# Usage: env_vars_del KEY
+env_vars_del() {
+  unset ENV_VARS["${1}"]
+}
+
+# env_vars_export_cmd creates a single "export K1=V1 K2=V2 ...;" output. If no
+# values are present, an empty output is generated.
+# Usage: env_vars_export_cmd
+env_vars_export_cmd() {
+  if [[ "${#ENV_VARS[@]}" -eq "0" ]]; then
+    echo ""
+    return
+  fi
+
+  declare -a pairs
+
+  for key in "${!ENV_VARS[@]}"; do
+    pairs+=("${key}=${ENV_VARS["$key"]}")
+  done
+
+  echo "export ${pairs[*]};"
+}
+
+# env_vars_subst replaces all previously defined environment variables in the
+# form of "@@ENV@@" by its value.
+# Usage: env_vars_subst echo hello @@USER_NAME@@
+env_vars_subst() {
+  for part in "${@}"; do
+    for key in "${!ENV_VARS[@]}"; do
+      part="${part/"@@${key}@@"/${ENV_VARS["$key"]}}"
+    done
+    printf '%s ' "$part"
+  done
+}

pimod.sh

@@ -5,6 +5,7 @@ set -euE
 pushd "$(dirname "$0")" > /dev/null
 
 . ./modules/chroot.sh
+. ./modules/env.sh
 . ./modules/error.sh
 . ./modules/esceval.sh
 . ./modules/from_remote.sh

stages/00-commands.sh

@@ -57,6 +57,10 @@ WORKDIR() {
   :
 }
 
+ENV() {
+  :
+}
+
 RUN() {
   :
 }

stages/30-chroot.sh

@@ -60,6 +60,39 @@ WORKDIR() {
   echo -e "\033[0;32m### WORKDIR ${WORKDIR_PATH}\033[0m"
 }
 
+# ENV either sets or unsets an environment variable to be used within the image.
+# If two parameters are given, the first is the key and the second the value.
+# If one parameter is given, the environment variable will be removed.
+#
+# An environment variable can be either used via $VAR within another sub-shell
+# (sh -c 'echo $VAR') or substituted beforehand via @@VAR@@.
+#
+# Usage: ENV KEY [VALUE]
+ENV() {
+  local key=""
+  local value=""
+
+  case "$#" in
+    "1")
+      key="$1"
+      env_vars_del "$key"
+      ;;
+
+    "2")
+      key="$1"
+      value="$2"
+      env_vars_set "$key" "$value"
+      ;;
+
+    *)
+      echo -e "\033[0;31m### Error: ENV KEY [VALUE]\033[0m"
+      return 1
+      ;;
+  esac
+
+  echo -e "\033[0;32m### ENV ${key}=${value}\033[0m"
+}
+
 # RUN executes a command in the chrooted image based on QEMU user emulation.
 #
 # Caveat: because the Pifile is just a Bash script, pipes do not work as one
@@ -69,8 +102,12 @@ WORKDIR() {
 # Usage: RUN CMD PARAMS...
 RUN() {
   echo -e "\033[0;32m### RUN ${*}\033[0m"
+
+  local cmd_esceval="$(esceval "$@")"
+  local cmd_env_subst="$(env_vars_subst "$cmd_esceval")"
+
   PATH=${GUEST_PATH} chroot "${CHROOT_MOUNT}" \
-    /bin/sh -c "cd ${WORKDIR_PATH}; $(esceval "$@")"
+    /bin/sh -c "cd ${WORKDIR_PATH}; $(env_vars_export_cmd) ${cmd_env_subst}"
 }
 
 # HOST executed a command on the local host and can be used to prepare files,