Use PROMPT_COMMAND as an array

dotlib/cattle.sh

@@ -24,5 +24,5 @@ kill-reaper() {
   done
 } &
 
-reaper_pid=$! prompt_cmds+=(ping-timer)
+reaper_pid=$! PROMPT_COMMAND+=(ping-timer)
 trap kill-reaper EXIT

dotlib/prompt.sh

@@ -27,14 +27,6 @@ elif (( 10#$month == 12 && 10#$day < 26 )); then
 fi
 
 setup-prompt() {
-  local cmd
-
-  if [[ -v prompt_cmds[@] ]]; then
-    for cmd in "${prompt_cmds[@]}"; do
-      "$cmd"
-    done
-  fi
-
   if [[ -d .git ]]; then
     git_branch="$(command git branch --show-current) "
   else
@@ -42,7 +34,7 @@ setup-prompt() {
   fi
 }
 
-PROMPT_COMMAND=setup-prompt
+PROMPT_COMMAND+=(setup-prompt)
 PS1='\w $git_branch'
 
 if [[ -v SSH_CLIENT ]]; then