New Feature: Creating a default Variables JSON from environment variables (#469)

Author: thedhruvn

README.md

@@ -109,6 +109,7 @@ Typically, each property is configured instead by the UPPER_SNAKE_CASE equivalen
 - `EMIT_SERVER_TELEMETRY`
 - `MSA_GAMERTAGS_ONLY`
 - `ITEM_TRANSACTION_LOGGING_ENABLED`
+- `VARIABLES`
 
 For example, to configure a flat, creative server instead of the default use:
 
@@ -191,6 +192,29 @@ There are various tools to look XUIDs up online and they are also printed to the
 -e ALLOW_LIST_USERS="player1:1234567890,player2:0987654321"
 ```
 
+## Variables
+
+Custom server variables are supported by Bedrock. Details and usage instructions can be found on the official bedrock documentation, located here:
+
+- [Variables & Secrets - Minecraft Creator Docs](https://learn.microsoft.com/en-us/minecraft/creator/documents/scriptingservers?view=minecraft-bedrock-stable#variables-and-secrets)
+- [Variables & Secrets - minecraft/server-admin example](https://learn.microsoft.com/en-us/minecraft/creator/scriptapi/minecraft/server-admin/serversecrets?view=minecraft-bedrock-experimental#getplayerprofilets-1)
+
+Custom server variables are passed in as comma-separated simple key-value pairs or as a full JSON string.
+
+Server variables are parsed into their most likely type (number-like turn into numbers, all other inputs are treated as string) using [jq's `fromjson` command](https://jqlang.github.io/jq/manual/#convert-to-from-json). In the example below, `var1` is a string, `var2` is a number, and `var3` is a string. 
+
+For greater control on types, users can provide a full string JSON representation that is used as-is.
+
+All variables are written to the variables file located at `config/default/variables.json`. There is no support for Module-specific variable handling at this time.
+
+```shell
+# passing in simple expressions
+-e VARIABLES="var1=customStringValue,var2=1234,var3=true"
+
+# pass in a full json object:
+-e VARIABLES='{"mobSpawnRate":22,"enableCheats":true,"worldArray":["My World", "Abc", 123]}'
+```
+
 ## Mods Addons
 
 Also known as behavior or resource packs, in order to add mods into your server you can follow these steps, tested with [OPS (One Player Sleep)](https://foxynotail.com/addons/ops/) and [bedrocktweaks](https://bedrocktweaks.net/resource-packs/)

bedrock-entry.sh

@@ -179,6 +179,34 @@ if [[ -n "$ALLOW_LIST_USERS" || -n "$WHITE_LIST_USERS" ]]; then
   fi
 fi
 
+if [[ -n "$VARIABLES" ]]; then
+  echo "Setting variables"
+  mkdir -p config/default
+
+  # Try to parse VARIABLES as JSON
+  if echo "$VARIABLES" | jq empty >/dev/null 2>&1; then
+    # VARIABLES is valid JSON
+    echo "$VARIABLES" | jq '.' > "config/default/variables.json"
+  else
+    # VARIABLES is not valid JSON, attempt to parse as custom format
+    echo "VARIABLES is not valid JSON, attempting to parse as custom format"
+
+    # Parse the VARIABLES using custom format (key:value,key:value)
+    # Note: Values should not contain unescaped commas or colons
+    jq -n --arg vars "$VARIABLES" '
+      $vars
+      | split(",")
+      | map(
+          split("=") as $kv |
+          { ($kv[0]): ($kv[1] | fromjson? // $kv[1]) }
+        )
+      | add
+    ' > "config/default/variables.json"
+  fi
+fi
+
+
+
 # prevent issue with bind mounted server.properties which can not be moved (sed tries to move the file when '-i' is used)
 _SERVER_PROPERTIES=$(sed '/^white-list=.*/d' server.properties) #Removes white-list= line from server.properties
 echo "${_SERVER_PROPERTIES}" > server.properties