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My Own Personal Additions to Emacs

Abstract

In the ten years that I have used the Emacs editor, I have written approximately 18,000 lines of Emacs Lisp to customise the program so that it behaves exactly like how I want it to. This article presents six additions to Emacs (my most important customisations) that I have made in the form of eight Emacs Lisp (*.el) files. The Lisp files presented in this document should work on all dialects of Emacs, including but not limited to Gnu Emacs and XEmacs. Please email me if you encounter any problems installing these files in your local Emacs system. The files linked to from this document fall under the Gnu General Public License.

1. How to install these features

To install an arbitrary Emacs Lisp file foo.el to your own local Emacs system, simply copy foo.el to one of the directories pointed to by the variable load-path and add the line (require 'foo) to your .emacs file. If you do not already have a .emacs file, create one in the directory that the environment variable HOME points to. If your HOME variable is not set, as might be the case if you are using Microsoft Windows, then you first need to set it to a appropriate value for your system. Examples of sensible values for HOME on Windows systems include c:/ or c:/home or d:/ (if your d:/ drive is a hard disk) or whatever. It is important that the directory pointed to by HOME actually exists, so you can put your .emacs file into it.

2. An automated backup system

Here are the features of my automated backup system:

Puts timestamps on archive (*.tar, *.tar.gz and *.zip) files if they don't already have one.
Keeps all but the latest N timestamped archive files, where N is an arbitrary positive integer.
Copies the latest archive files to a different hard drive for a poor man's R.A.I.D. (Redundant Array of Inexpensive Disks) system.
Searches for files that the hard drive corrupts, deletes or renames because of hardware failure.

The file bak.el contains the following important functions:

datify-dir takes an argument dirname and for each file in directory dirname timestamps it with the current date and time. For example, if there is a file foo.tar in the directory dirname, then it renames it to foo-YYYYMMDD-hhmmss.tar where the following apply (in order): YYYY is the current year, MM is the current month, DD is the current day of the month, hh is the current hour (in a 24 hour clock), mm is the current minute and ss is the current second.
cull-duplicates takes a directory argument dirname and an integer number-to-keep and deletes all but the latest number-to-keep files for each archive.

The file bak-windows.el contains the function bak-windows--copy-to-c-drive copies the latest archives from my d:/ drive to my c:/ drive.

The file checksum.el has the command M-x checksum which searches for files that have been corrupted, deleted or renamed. This system was invented out of necessity as one of my hard drives started behaving erratically, most likely due to overheating. The command computes the 32-bit checksum of the file, internally calling the Gnu Shell Command cksum and comparing it with the corresponding value in the Database of Checksums which is a collection of checksums each taken after the last time each file was saved within Emacs. Note that modification of files outside of Emacs will cause a false positive. If that happens, then the Database of Checksums needs to be rebuilt. Most implementations of Emacs can only store 28-bit integers but this only weakens the error detecting capabilities of the system by a factor of 2³² / 2²⁸ = 16. To use my system, you will need to redefine the function checksum--get-file-list to choose the files that you wish to include in the system.

3. A C++ class browser

The file cbrow.el (cbrow stands for Class Browser) implements a C++ class browser. Pressing f5 inside a method of a source file (e.g. *.cpp or *.cc) takes you to corresponding line for that function in the the header file for that class. Pressing enter at this point takes you back to the source file. Otherwise pressing f5 takes you to a summary list of all the classes in your program. To use this code, you will need to customise the function cbrow--init which can be found at the end of cbrow.el.

4. A recoverable file deletion system

The file trashcan.el contains a recoverable file deletion system that behaves like the trash can or recycle bin that many operating systems, present and past, show on their screens. This system creates special directories known as trashcan directories to hold files that can be deleted or undeleted (restored/recovered). On Unix systems there is one trashcan directory for each user and the default values are $HOME/.TRASHCAN for each value of $HOME. On Windows systems there are trashcan directories at the following default locations: a:\TRASHCAN, b:\TRASHCAN, c:\TRASHCAN etc.

This system changes the behaviour of the "x" key in dired mode from permanently deleting files to a two stage system. If you are not in a trashcan directory, then the selected files are moved into a trashcan directory. If you are already in a trashcan directory, the the selected files are permanently deleted. Files in a trashcan directory can be restored by viewing that directory in dired mode, selecting some files and executing the command M-x trashcan-restore. All of the files in a trashcan directory can also be permanently deleted in one hit by issuing the command M-x trashcan-empty. The name "trashcan" comes from my old Amiga Computer which I still have fond memories of! Click here to download a tarball containing trashcan.el.

Note: This code has been submitted to the Emacs Lisp List at Cambridge University, England.

5. The current function/method on the mode-line

The file cfm.el (cfm stands for Current Function/Method) causes the current function (C/C++) or method (C++/Java) to be printed on the modeline. This is useful when you are inside a large method and you can't remember which function/method you are in.

6. An integrity checker for burnt CD's

The file archive-compare.el contains the function archive-compare--zips that checks the integrity of CD's burnt using my CD burner. This function makes use of the Five Minute Principle which is used by builders to assess the quality of their buildings: if the building stays erect for five minutes after completion, then it will remain erect forever! Translated to the operation of the integrity checker: if the data is still intact after five minutes after the CD is burnt, then it will remain intact for a long time. Internally this function executes the my own shell command compare-files.cc which takes two file arguments, compares them and prints the result of the comparison to std::cout.

7. Some useful directory functions

The file directory-files-deep.el contains the following useful functions that generalise the built-in function directory-files:

directory-files-no-dotdotdot omits the directories "." and "..".
directory-files-subdirs only lists subdirectories.
directory-files-no-subdirs only lists non-subdirectories and omits the directories "." and "..".
directory-files-deep lists all the files in the given directory plus any files in any subdirectories (direct or indirect) of that directory, minus the directories "." and "..".

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