borgmatic/backup.sh - fix printf bug

Interpolation can and does insert % placeholders into the printf
template text - although not valid ones as they're intended for
python.

So be more careful!  Put all inserted text into the parameters to
printf, or use echo.

Also, keep some of the alterations used whilst diagnosing this.

templates/docker-compose/borgmatic/backup.sh

@@ -21,8 +21,8 @@ PARAM="$1"
 
 # Helper function to prepend a timestamp and the first parameter to every line of STDIN
 indent() {
-    while read -rs line; do
-        printf "%s%s%s\n" "$(date -Iminutes)" "${1:- }" "$line"
+    while IFS='' read -rs line; do
+        echo "$(date -Iminutes)${1:- }$line"
     done
 }
 
@@ -37,14 +37,15 @@ log() {
 
 report() {
     if [ "$RESULT" = "0" ]; then
-        log echo "SUCCESS"
+        log echo "SUCCESS!"
         PREFIX="$SUCCESS_PREFIX"
     else
         log echo "FAILED: $RESULT"
         PREFIX="$FAILED_PREFIX"
     fi
-    printf "Subject: $PREFIX: '$PARAM'\n\n$(cat $LOGFILE)\n" |
+    printf "Subject: %s: '%s'\n\n%s\n" "$PREFIX" "$PARAM" "$(cat $LOGFILE)" |
         sendmail -t "$MAIL_TO"
+    log echo "Report sent."
 }
 
 testmail() {
@@ -60,8 +61,9 @@ failed() {
 
 cleanup() {
     borgmatic break-lock
-    echo "Done, removing $LOGFILE"
+    echo "Removing $LOGFILE"
     rm -f "$LOGFILE"
+    echo "Exiting."
 }
 
 # Handle various kinds of exit
@@ -86,9 +88,14 @@ case  "$PARAM" in
         RESULT=$?
         report
         ;;
+    dummy-run)
+        log echo STARTED: dummy-run
+        borgmatic nonesuch
+        RESULT=$?
+        report
+        ;;
     *)
         log echo "UNKNOWN COMMAND: '$PARAM'"
         report
         ;;
 esac
-