subcommand restructure and bashstyle refactor. closes #1579

plugins/shell/commands

@@ -1,53 +1,8 @@
 #!/usr/bin/env bash
-[[ " shell help shell:help " == *" $1 "* ]] || exit "$DOKKU_NOT_IMPLEMENTED_EXIT"
+[[ " help shell:help " == *" $1 "* ]] || exit "$DOKKU_NOT_IMPLEMENTED_EXIT"
 set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
 
 case "$1" in
-  shell)
-    INPUTRC="$PLUGIN_ROOT/inputrc"
-    HISTFILE=~/.dokku_history
-
-    history -r || true
-
-    trim()
-    {
-      sed -e 's/^[[:space:]]*//g' -e 's/[[:space:]]*$//g'
-    }
-
-    trap 'history -w' EXIT
-
-    while true; do
-      trap '' SIGINT
-      read -rep "dokku> " line || {
-        echo; true; break
-      }
-      trap - SIGINT
-
-      line=$(echo "$line" | trim)
-      CMD=$(echo "$line" | awk '{ print $1 }')
-
-      [[ -z $CMD ]] && continue
-
-      [[ "$line" != "$(fc -ln -1 | trim)" ]] && history -s "$line"
-
-      case $CMD in
-        # shell builtins
-        clear)
-          clear
-          ;;
-
-        quit|exit)
-          break
-          ;;
-
-        # Not a built-in, run as regular dokku command
-        *)
-          dokku "$line" || true
-      esac
-
-    done
-    ;;
-
   help | shell:help)
     cat<<EOF
     shell, Spawn dokku shell

plugins/shell/subcommands/default

@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+
+shell_cmd() {
+  local desc="dokku shell interpreter via command line"
+  local cmd="shell"
+  local INPUTRC="$PLUGIN_ROOT/inputrc"
+  local HISTFILE=~/.dokku_history
+
+  history -r || true
+
+  trim()
+  {
+    sed -e 's/^[[:space:]]*//g' -e 's/[[:space:]]*$//g'
+  }
+
+  trap 'history -w' EXIT
+
+  while true; do
+    trap '' SIGINT
+    read -rep "dokku> " line || {
+      echo; true; break
+    }
+    trap - SIGINT
+
+    local line=$(echo "$line" | trim)
+    local CMD=$(echo "$line" | awk '{ print $1 }')
+
+    [[ -z $CMD ]] && continue
+
+    [[ "$line" != "$(fc -ln -1 | trim)" ]] && history -s "$line"
+
+    case $CMD in
+      # shell builtins
+      clear)
+        clear
+        ;;
+
+      quit|exit)
+        break
+        ;;
+
+      # Not a built-in, run as regular dokku command
+      *)
+        # shellcheck disable=SC2086
+        dokku $line || true
+    esac
+
+  done
+}
+
+shell_cmd