templates/docker-compose/borgmatic/ - avoid losing STDERR lines

use stdbuf to change the buffereing mode to be linewise

templates/docker-compose/borgmatic/Dockerfile

@@ -1,4 +1,11 @@
 FROM b3vis/borgmatic:latest-msmtp
 
+# Install stdbuf, used by backup.sh
+RUN \
+  echo "* Installing Runtime Packages" \
+    && apk upgrade --no-cache \
+  && echo "* Installing Runtime Packages" \
+    && apk add -U --no-cache \
+      coreutils
 COPY --chmod=755 backup.sh /backup.sh
 

templates/docker-compose/borgmatic/backup.sh

@@ -31,7 +31,7 @@ indent() {
 log() {
     # Adapted from https://stackoverflow.com/a/31151808
     {
-        "$@"   2>&1 1>&3 3>&- | indent " ! "
+        stdbuf -oL -eL "$@"   2>&1 1>&3 3>&- | indent " ! "
     } 3>&1 1>&2 | indent " | " | tee -a "$LOGFILE"
 }