inject a shell script into another host and execute it (using dbclient)

inject.sh

DBCLIENT="$(which dbclient)"

[ -z "$INJECT_USERNAME" ] && INJECT_USERNAME="root"
[ -z "$INJECT_PASSWORD" ] && INJECT_PASSWORD="1q2w3e"

doremote() {
  DROPBEAR_PASSWORD="$INJECT_PASSWORD" "$DBCLIENT" -y -y -A -l "$INJECT_USERNAME" "$INJECT_HOST" "$@"
}

inject_progr() {
  echo -n '[ '
  case $? in
    0) echo 'ok ]' ;;
    *) echo 'failed ]'; return 1 ;;
  esac
}

# inject SOURCE
inject() {
  if [ -z "$1" ]; then
    echo 'USAGE: inject SOURCE'
    return 1
  fi

  local PSRC=".${1}.isp"
  local DEST='~/.'"$$_$(basename "$1")"
  echo "inject: $1 -> $PSRC -> $INJECT_USERNAME@$INJECT_HOST:$DEST"

  echo -n ' - patch '
  cp -f "$1" "$PSRC"
  if [ "$(tail -n 1 "$1")" != 'rm -f "$0"' ]; then
    echo 'rm -f "$0"' >> "$PSRC"
  fi
  [ -f "$PSRC" ]
  inject_progr || return 1

  echo -n ' - upload '
  cat "$PSRC" | doremote "cat > $DEST" &>/dev/null
  inject_progr || return 1

  echo ' - first clean'
  rm -f "$PSRC"
  echo -n ' - make executable '
  doremote "chmod +x $DEST" &>/dev/null
  inject_progr || return 1

  echo ' - execute'
  doremote "$DEST" 2>&1 | tail -n +3
  echo -n '   '
  inject_progr || return 1
}