Emacs auto save file

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Emacs的文件备份机制

本文是对这篇文章 Emacs的临时文件和备份文件 的细化和进一步说明.

临时文件(Auto-Save file)

正常情况下emacs退出后会删掉这个文件, 所以我觉得临时文件这个汉语名字更为准确一些. Auto-Save这个名字, 我开始以为是自动保存到原文件去的意思, 比如 ManateeLazyCat在“Emacs：我已经十年没有按过保存按键了” 里的意思。auto-save.el

但是用过一段上面的 auto-save.el 后, 我还是更喜欢emacs默认的保存方式. 由自己决定什么时候把缓冲区中的文件保存到原文件中去. 默认情况下, 如果输入超过300个字符或是键鼠无动作超过30秒, emacs就会自动把内存里的缓冲区变动保存到临时文件 #file-name# 中. 如果由于断电等原因emacs异常退出, 没来得及保存, 可以使用 M-x recover-file 来恢复文件.

可以设置自动保存的参数, 比如:

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(setq-default auto-save-timeout 15) ; 15秒无动作,自动保存
(setq-default auto-save-interval 100) ; 100个字符间隔, 自动保存

备份文件(Backup files)

因为会在原目录中留下 “file-name~“ , 所以大家都比较烦. 而且现在可以通过 git 管理版本, 所以一般关掉这个功能.

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(setq make-backup-files nil)

如果想保留这个功能, 又不想在当前目录下留下一堆 “file-name~“ 烦人, 可以指定集中保存备份文件的目录.

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(setq
     backup-by-copying t ; 自动备份
     backup-directory-alist
     '(("." . "~/.em_backup")) ; 自动备份在目录"~/.em_backup"下
     delete-old-versions t ; 自动删除旧的备份文件
     kept-new-versions 3 ; 保留最近的3个备份文件
     kept-old-versions 1 ; 保留最早的1个备份文件
     version-control t) ; 多次备份

自动备份文件有两种模式: 改名(Renaming)和复制(Copying). 默认是改名模式. 两种模式的区别可见 18.3.2.3 Copying vs. Renaming . 只有文件存在硬链接而且有多个文件名的情况下, 复制(Copying) 模式才有意义. 在改名模式下, 其他硬链接会依然链接到备份文件上. 而复制模式下, 其他硬链接会链接到新文件上.

打开复制模式:

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(setq backup-by-copying t) ;使用复制模式备份文件

参考:

https://stackoverflow.com/questions/151945/how-do-i-control-how-emacs-makes-backup-files

If you’ve ever been saved by an Emacs backup file, you probably want more of them, not less of them. It is annoying that they go in the same directory as the file you’re editing, but that is easy to change. You can make all backup files go into a directory by putting something like the following in your .emacs.

(setq backup-directory-alist `((“.” . “~/.saves”)))

There are a number of arcane details associated with how Emacs might create your backup files. Should it rename the original and write out the edited buffer? What if the original is linked? In general, the safest but slowest bet is to always make backups by copying.

(setq backup-by-copying t)

If that’s too slow for some reason you might also have a look at backup-by-copying-when-linked.

Since your backups are all in their own place now, you might want more of them, rather than less of them. Have a look at the Emacs documentation for these variables (with C-h v).

(setq delete-old-versions t kept-new-versions 6 kept-old-versions 2 version-control t)

Finally, if you absolutely must have no backup files:

(setq make-backup-files nil)

It makes me sick to think of it though.