feat(BASH): add env var override library

cicd-tools/boxes/0.1.0/libraries/override.sh

@@ -0,0 +1,82 @@
+#!/bin/bash
+
+# Library for allowing environment variables to override configured settings.
+
+set -eo pipefail
+
+# shellcheck source=./logging.sh
+source "$(dirname -- "${BASH_SOURCE[0]}")/logging.sh"
+
+override() {
+  local OVERRIDES=()
+  local TARGETS=()
+
+  log "DEBUG" "${BASH_SOURCE[0]} '$*'"
+
+  _override_args "$@"
+  _override_set_values
+}
+
+_override_args() {
+  local OPTARG
+  local OPTIND
+  local OPTION
+
+  while getopts "o:t:" OPTION; do
+    case "$OPTION" in
+      o)
+        _override_parse_overrides "${OPTARG}"
+        ;;
+      t)
+        _override_parse_targets "${OPTARG}"
+        ;;
+      \?)
+        _override_usage
+        ;;
+      :)
+        _override_usage
+        ;;
+    esac
+  done
+
+  if [[ "${#OVERRIDES[@]}" -ne "${#TARGETS[@]}" ]]; then
+    log "ERROR" "OVERRIDE > You must specify the same number of OVERRIDE environment variables and OPTIONAL environment variables!"
+    exit 127
+  fi
+}
+
+_override_parse_overrides() {
+  log "DEBUG" "OVERRIDE > Parsing OVERRIDE environment variable values."
+  # shellcheck disable=SC2034
+  IFS=' ' read -r -a OVERRIDES <<< "${1}"
+}
+
+_override_parse_targets() {
+  log "DEBUG" "OVERRIDE > Parsing TARGET environment variable values."
+  # shellcheck disable=SC2034
+  IFS=' ' read -r -a TARGETS <<< "${1}"
+}
+
+_override_set_values() {
+  local INDEX=-1
+  local OVERRIDE_VARIABLE
+
+  for OVERRIDE_VARIABLE in "${OVERRIDES[@]}"; do
+    ((INDEX++)) || true
+    if [[ -z "${!OVERRIDE_VARIABLE}" ]]; then
+      log "DEBUG" "OVERRIDE > No override specified for '${OVERRIDE_VARIABLE}' ..."
+    else
+      eval "${TARGETS[${INDEX}]}"="${!OVERRIDE_VARIABLE}"
+      log "WARNING" "OVERRIDE > Variable '${TARGETS[${INDEX}]}' now overridden with '${!OVERRIDE_VARIABLE}' ..."
+    fi
+  done
+}
+
+_override_usage() {
+  log "ERROR" "override.sh -- an interface to override internal values with environment variables."
+  log "ERROR" "-----------------------------------------------------------------------------------"
+  log "ERROR" "override.sh"
+  log "ERROR" "           -o (SPACE SEPARATED LIST OF OVERRIDE ENV VARS)"
+  log "ERROR" "           -t (SPACE SEPARATED LIST OF TARGET OVERRIDE_VARIABLES THAT WILL BE OVERRIDDEN)"
+  exit 127
+}