btrbk-mail: optionally prefix command output lines

Add configurable prefix for each line of command output. Seems wrong,
but outsmarts the mail clients.

The problem is that some (most?) mail clients outsmart the specs and
replace text/plain mails by quotations, emoticons, emphasis, ...
The only "correct" solution is to disable these features in the mail
client.

Acceptable workaround for #376.

contrib/cron/btrbk-mail

@@ -48,6 +48,14 @@ btrbk_command="run"
 btrbk_opts="-c /etc/btrbk/btrbk.conf"
 
 
+### Layout options:
+
+# Prefix command output: useful when using mail clients displaying
+# btrbk summary lines starting with ">>>" as quotations.
+#mail_cmd_block_prefix='\\u200B' # zero-width whitespace
+#mail_cmd_block_prefix=". "
+
+
 #####  end config section  #####
 
 
@@ -127,18 +135,32 @@ die()
     exit 1
 }
 
+run_cmd()
+{
+    cmd_out=$("$@" 2>&1)
+    local ret=$?
+    detail+="++ ${@@Q}\n"
+    if [[ -n "${mail_cmd_block_prefix:-}" ]] && [[ -n "$cmd_out" ]]; then
+        detail+=$(echo -n "$cmd_out" | sed "s/^/${mail_cmd_block_prefix}/")
+        detail+="\n"
+    else
+        detail+=$cmd_out
+    fi
+    return $ret
+}
+
 mount_all()
 {
     # mount all mountpoints listed in $mount_targets
     mounted=""
     for mountpoint in $mount_targets; do
         ebegin "Mounting $mountpoint"
-        detail+=`(set -x; findmnt -n $mountpoint) 2>&1`
+        run_cmd findmnt -n $mountpoint
         if [[ $? -eq 0 ]]; then
             eend -1 "already mounted"
         else
             detail+="\n"
-            detail+=`(set -x; mount --target $mountpoint) 2>&1`
+            run_cmd mount --target $mountpoint
             eend $? && mounted+=" $mountpoint"
         fi
     done
@@ -148,7 +170,7 @@ umount_mounted()
 {
     for mountpoint in $mounted; do
         ebegin "Unmounting $mountpoint"
-        detail+=`(set -x; umount $mountpoint) 2>&1`
+        run_cmd umount $mountpoint
         eend $?
     done
 }
@@ -170,22 +192,19 @@ for key in $rsync_enable; do
         # NOTE: This also appends the stats to the log file (rsync_log).
         # Another approach to count the files would be something like:
         # "rsync --out-format='' | wc -l"
-        ret=`(set -x; \
-              rsync ${rsync_opt[$key]} \
+        run_cmd rsync ${rsync_opt[$key]} \
                     --info=stats2 \
                     ${rsync_log[$key]:+--log-file="${rsync_log[$key]}"} \
                     ${rsync_rsh[$key]:+-e "${rsync_rsh[$key]}"} \
                     "${rsync_src[$key]}" \
                     "${rsync_dst[$key]}"
-             ) 2>&1`
         exitcode=$?
-        detail+=$ret
 
         # parse stats2 (count created/deleted/transferred files)
         REGEXP=$'\n''Number of created files: ([0-9]+)'
         REGEXP+='.*'$'\n''Number of deleted files: ([0-9]+)'
         REGEXP+='.*'$'\n''Number of regular files transferred: ([0-9]+)'
-        if [[ $ret =~ $REGEXP ]]; then
+        if [[ $cmd_out =~ $REGEXP ]]; then
             rsync_stats="${BASH_REMATCH[1]}/${BASH_REMATCH[2]}/${BASH_REMATCH[3]}"
             rsync_stats_long="${BASH_REMATCH[1]} created, ${BASH_REMATCH[2]} deleted, ${BASH_REMATCH[3]} transferred"
             nfiles=$(( ${BASH_REMATCH[1]} + ${BASH_REMATCH[2]} + ${BASH_REMATCH[3]} ))
@@ -225,7 +244,7 @@ fi
 #
 if [[ ${#sync_fs[@]} -gt 0 ]]; then
     ebegin "Syncing filesystems at ${sync_fs[@]}"
-    detail+=`(set -x; sync -f "${sync_fs[@]}") 2>&1`
+    run_cmd sync -f "${sync_fs[@]}"
     eend $?
 fi
 
@@ -234,7 +253,7 @@ fi
 # run btrbk
 #
 ebegin "Running btrbk"
-detail+=`(set -x; btrbk ${btrbk_opts:-} ${btrbk_command}) 2>&1`
+run_cmd btrbk ${btrbk_opts:-} ${btrbk_command}
 exitcode=$?
 case $exitcode in
     0)  status="All backups successful"