fail instead of looping when no mount target can be read

pbc

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+set -o pipefail
+
 function usage() {
   local full=${1:-false}
   cat <<EOF
@@ -181,24 +183,27 @@ function may_select() {
 }
 
 function select_group() {
-  local groups
-  readarray -t groups < <(get_group_names)
-  (( ${#groups[@]} == 0 )) && return 2
+  local groups raw
+  raw=$(get_group_names) || { echo "Error: failed to query PBS!" >&2; return 1; }
+  [ -z "$raw" ] && return 2
+  readarray -t groups <<< "$raw"
 
   PS3="Snapshot group [1-${#groups[@]}]: "
   GROUP=$(may_select "$1" "${groups[@]}") || { echo "Error: invalid group" >&2; return 1; }
 }
 
 function select_snapshot_and_archive() {
-  local snapshots archives
-  readarray -t snapshots < <(get_snapshot_names)
-  (( ${#snapshots[@]} == 0 )) && return 2
+  local snapshots archives raw
+  raw=$(get_snapshot_names) || { echo "Error: failed to query PBS!" >&2; return 1; }
+  [ -z "$raw" ] && return 2
+  readarray -t snapshots <<< "$raw"
 
   PS3="Snapshot [1-${#snapshots[@]}]: "
   SNAPSHOT=$(may_select "$1" "${snapshots[@]}") || { echo "Error: invalid snapshot" >&2; return 1; }
 
-  readarray -t archives < <(get_snapshot_files "$SNAPSHOT")
-  (( ${#archives[@]} == 0 )) && return 3
+  raw=$(get_snapshot_files "$SNAPSHOT") || { echo "Error: failed to query PBS!" >&2; return 1; }
+  [ -z "$raw" ] && return 3
+  readarray -t archives <<< "$raw"
 
   PS3="Archive [1-${#archives[@]}]: "
   ARCHIVE=$(may_select "$2" "${archives[@]}") || { echo "Error: invalid archive" >&2; return 1; }
@@ -355,9 +360,10 @@ case "$action" in
     target=${args[2]}
 
     if [ -z "$target" ]; then
+      [ ! -t 0 ] && echo "Error: no target path given and stdin is not a terminal" >&2 && exit 1
       while [ -z "$target" ]; do
         echo -n "Target path: "
-        read -r target
+        ! read -r target && [ -z "$target" ] && echo "Error: no target path given" >&2 && exit 1
         [ -d "$target" ] && break
         echo -e "\nError: $target: no such directory\n" >&2
         target=''