====================================
While statements
====================================

while something happens; do
  echo a
  echo b
done

---

(program
  (while_statement
    (command (command_name) (argument))
    (do_group
      (command (command_name) (argument))
      (command (command_name) (argument)))))

====================================
If statements
====================================

if cat some_file | grep -v ok; then
  echo one
elif cat other_file | grep -v ok; then
  echo two
else
  exit
fi

---

(program
  (if_statement
    (pipeline
      (command (command_name) (argument))
      (command (command_name) (argument) (argument)))
    (command (command_name) (argument))
    (elif_clause
      (pipeline
        (command (command_name) (argument))
        (command (command_name) (argument) (argument)))
      (command (command_name) (argument)))
    (else_clause
      (command (command_name)))))