SHELL_SCRIPT
  COMMANDS_LIST
    GENERIC_COMMAND_DIRECTIVE
      PsiElement($)('$')
      SHELL_PARAMETER_EXPANSION
        PsiElement({)('{')
        PsiElement(word)('B')
        PsiElement(param_separator)(':-')
        PsiElement($)('$')
        SHELL_PARAMETER_EXPANSION
          PsiElement({)('{')
          PsiElement(word)('a')
          PsiElement(})('}')
        PsiElement(})('}')