Allowed CF_BASE_DIR/FTB_BASE_DIR to be configured

For #518

README.md

@@ -535,6 +535,12 @@ The following example uses `/modpacks` as the container path as the pre-download
         -e CF_SERVER_MOD=/modpacks/SkyFactory_4_Server_4.1.0.zip \
         -p 25565:25565 -e EULA=TRUE --name mc itzg/minecraft-server
 
+#### Modpack data directory
+
+By default, CurseForge modpacks are expanded into the sub-directory `/data/FeedTheBeast` and executed from there. (The default location was chosen for legacy reasons, when Curse and FTB were maintained together.)
+
+The directory can be changed by setting `CF_BASE_DIR`, such as `-e CF_BASE_DIR=/data`.
+
 #### Buggy start scripts
 
 Some modpacks have buggy or overly complex start scripts. You can avoid using the bundled start script and use this image's standard server-starting logic by adding `-e USE_MODPACK_START_SCRIPT=false`.
@@ -1125,4 +1131,4 @@ To run this image on a RaspberryPi 3 B+, 4, or newer, use the image tag
 
     itzg/minecraft-server:multiarch
 
-> NOTE: you may need to lower the memory allocation, such as `-e MEMORY=750m`
+> NOTE: you may need to lower the memory allocation, such as `-e MEMORY=750m`

start-deployCF

@@ -5,7 +5,9 @@ set -e
 . ${SCRIPTS:-/}start-utils
 isDebugging && set -x
 
-export FTB_BASE_DIR=/data/FeedTheBeast
+: ${FTB_BASE_DIR:=${CF_BASE_DIR:-/data/FeedTheBeast}}
+export FTB_BASE_DIR
+
 legacyJavaFixerUrl=https://ftb.forgecdn.net/FTB2/maven/net/minecraftforge/lex/legacyjavafixer/1.0/legacyjavafixer-1.0.jar
 export TYPE=FEED-THE-BEAST