命令組成

由於emacs本身就是emacs lisp編寫的，所以在emacs中一個命令其實就是一個函式。

(defun helm-M-x (_arg &optional command-name)
"Preconfigured `helm' for Emacs commands.
It is `helm' replacement of regular `M-x' `execute-extended-command'.
Unlike regular `M-x' emacs vanilla `execute-extended-command' command,
the prefix args if needed, can be passed AFTER starting `helm-M-x'.
When a prefix arg is passed BEFORE starting `helm-M-x', the first `C-u'
while in `helm-M-x' session will disable it.

You can get help on each command by persistent action."

快捷鍵	命令	說明
M-!	shell-command	使用系統shell 執行命令並輸出到buffer "Shell Command Output"
M-	shell-command-on-region	執行Shell命令並輸出到編輯區域
M-x	helm-M-x	執行emacs命令
-	term	開啟buffer"terminal",執行終端
-	eshell	建立一個互動式的Elisp shell。

可以通過設定shell-file-name變數的值來改變預設shell

 (setq shell-file-name "/bin/bash")

eshell的用法

elisp

快速入門

掌握基本語法規則後就應該多看人家寫的程式碼！
利用edebug更好更快地理解程式碼
假如想要知道開啟檔案是怎麼操作的。

1. 首先定位函式的程式碼。

   • 已知快捷鍵C-x C-f。依次鍵入C-h k C-x C-f。
     然後就會顯示函式的資訊，點選helm-files.el就能看到程式碼。

   • 如果不知道快捷鍵，則鍵入C-h a ，利用命令的名稱來搜尋可能的選項。

   (defun helm-find-files (arg)
     "Preconfigured `helm' for helm implementation of `find-file'.
   Called with a prefix arg show history if some.
   Don't call it from programs, use `helm-find-files-1' instead.
   This is the starting point for nearly all actions you can do on files."
     (interactive "P")
     (let* ((hist            (and arg helm-ff-history (helm-find-files-history)))
            (smart-input     (or hist (helm-find-files-initial-input)))
            (default-input   (expand-file-name (helm-current-directory)))
            (input           (cond (helm-find-file-ignore-thing-at-point
                                    default-input)
                                   ((and (eq major-mode 'org-agenda-mode)
                                         org-directory
                                         (not smart-input))
                                    (expand-file-name org-directory))
                                   ((and (eq major-mode 'dired-mode) smart-input)
                                    (file-name-directory smart-input))
                                   ((and (not (string= smart-input ""))
                                         smart-input))
                                   (t default-input)))
            (input-as-presel (null (nth 0 (file-attributes input))))
            (presel          (helm-aif (or hist
                                           (and input-as-presel input)
                                           (buffer-file-name (current-buffer))
                                           (and (eq major-mode 'dired-mode)
                                                smart-input))
                                 (if helm-ff-transformer-show-only-basename
                                     (helm-basename it) it))))
       (set-text-properties 0 (length input) nil input)
       (helm-find-files-1 input (and presel (null helm-ff-no-preselect)
                                     (concat "^" (regexp-quote presel))))))

2. 將游標放到函式名上，鍵入 C-u C-M-x可新增中斷入口。M-x edebug-mod開啟後會在選單欄多出edebug的選項。

3. 使用命令C-x C-f便會觸發中斷。

4. n可單步執行

IELM

這是一個很方便的工具。不同於M-x只能呼叫命令，IELM可以使用lisp語言，對於實現emacs擴充套件實在是太便捷了！

更多更詳細的內容還是得看文件！！