================================================================================
Command Substitudion - simple
================================================================================

echo (printf text)
echo (begin; print 1; end;;;)
echo (;;;)
echo ()

--------------------------------------------------------------------------------

(program
  (command
    name: (word)
    argument: (command_substitution
      (command
        name: (word)
        argument: (word))))
  (command
    name: (word)
    argument: (command_substitution
      (begin_statement
        (command
          name: (word)
          argument: (integer)))))
  (command
    name: (word)
    argument: (command_substitution))
  (command
    name: (word)
    argument: (command_substitution)))

================================================================================
Command Substitudion - multiline
================================================================================

echo (
    printf text
)
echo (
    printf text
    printf ' ing'
)

--------------------------------------------------------------------------------

(program
  (command
    name: (word)
    argument: (command_substitution
      (command
        name: (word)
        argument: (word))))
  (command
    name: (word)
    argument: (command_substitution
      (command
        name: (word)
        argument: (word))
      (command
        name: (word)
        argument: (single_quote_string)))))
