TIL-Emacs

This page now lives here

Today I learned, Emacs version. More of a mini blog. Inspired by jbranchaud/til.

• org macros

  Org mode allows simple text replacement macros with arguments for export. See more here.

• benchmark-run

  Just what you expect. Learnt from here. Also check benchmark-run-compiled if you want to compare compiled elisp performance.

• calc

  Emacs has a very elaborate calculator capable even of symbolic mathematics and manipulation. Check this blog post by Chris to get a feel. I used to call insect to perform unit conversions, but looks like calc is enough.

• tail calls

  Emacs lisp doesn’t optimize tail calls. This forces you to use loops (like while) instead of recursion. Two workarounds are tco and recur.

• two columns

  Two column editing lets you split the current buffer in two columns (obviously) which are finally merged in one. I am trying to use it for writing sidenotes in org files. Will have issues with org-export though.

• gap buffers

  Emacs internally uses gap buffers to represent text (in buffers). Current gap values can be accessed using functions gap-position and gap-size. See the page on manual for more.

• reverse variable search

  Weird but possibly useful. apropos-value lets you search for variables with provided value.

• literate configuration

  Using org-babel-load-file, you can load emacs-lisp snippets from an org file. This is great for maintaining readable configuration like done in emacs24-starter-kit.

• image tooltips

  Its possible to show image inside the regular emacs tooltips. This is handy for documents with linked images.

• capturing buffer bookmarks

  Org capture has templates (%a, %A etc.) for capturing the location where the org-capture was called. This comes in handy with emails, todos in code etc.

• narrow region

  Narrowing allows showing only a certain part of a buffer instead of full content. This lets you work on the narrowed region without affecting other stuff.

• org-edit-special

  Special chunks in org mode like babel source blocks can be edited in a separate dedicated buffer using org-edit-special.

• rectangle insert

  Iedit has a iedit-rectangle-mode which lets edit vertical chunks. Handy for enforcing indentation over a section.

• undo-tree

  undo-tree maintains a tree instead of a linear undo/redo history. Wish there was something similar for krita/gimp.

• org-store-link

  Special bookmarks to different modes can be saved in org files using org-store-link and org-insert-link.

• common lisp emulation

  Elisp can simulate many features of common lisp, including full fledged function arguments, using the cl package.

• winner-mode

  Probably too late to know about it. Winner mode lets you undo/redo window configuration.

• file-watch

  file-notify-add-watch allows hooking up callbacks for file changes.

• re-builder

  Emacs lets you check regex on the fly in current buffer using re-builder.

• obarray

  obarray refers to a vector of symbols which are interned and is used for looking up value of symbols.

• latex fragment preview

  Latex code snippets can be previewed directly in org-mode using org-toggle-latex-fragment.

• dired drag and drop

  Dropping a file to a dired buffer copies stuff to it.

• advising functions

  Elisp lets you add a custom behavior on an already existing function using the advising facility.

• highlight-regexp

  Highlight a regexp in buffer with certain color using highlight-regexp.

• eieio

  Emacs Lisp has an Object Oriented Programming system called EIEIO mimicking Common Lisp Object System.

• org-protocol

  org-protocol intercepts calls from emacsclient to trigger custom actions without external dependencies. Only one protocol has to be configured with your external applications or the operating system, to trigger an arbitrary number of custom actions. Just register your custom sub-protocol and handler with the variable `org-protocol-protocol-alist’.

  Taken from here. Probably the best surprise feature I found till date.

• comint mode scroll

  Comint mode (all the shell-ish processes), by default (in spacemacs at least), shows everything possible whenever a shell output comes out. This results in pushing (scrolling) the current line to the bottom even when you were up somewhere. This can be fixed by setting comint-scroll-show-maximum-output to nil.

• custom agenda views

  Org agenda view allows custom built views by customizing the variable org-agenda-custom-commands. The customization lets you work with separate files, tags, todo-states and much more.

• current-prefix-arg

  Setting current-prefix-arg variable works as C-u key for the command in scope. This allows wrapping up some useful commands with prefix arguments.

• apropos

  Apropos commands (apropos, apropos-command etc.) do full text searches over corresponding components (symbols, commands, etc.) and are powerful and useful than the regular ways.

• caching sudo password in eshell

  Eshell can use tramp’s sudo instead of /usr/bin/sudo and then cache passwords. Setting alias by ~alias sudo ‘eshell/sudo $*’~ in eshell after setting up cache does the trick.

  (use-package em-tramp
    :config
    (setq eshell-prefer-lisp-functions t)
    (setq password-cache t)
    (setq password-cache-expiry 3600))
      

  Source

• syntax table

  Emacs maintains what are called syntax table for modes which define which character is going to be treated as what. As an example, you could set $ as a whitespace character to assist jumping around in text by using (modify-syntax-entry ?$ " ")

• ditaa & dot

  Babel has great support for ditaa and dot snippets, allowing creation of graph, drawings and flowcharts easily.

• lexical scoping

  Adding ;;; -*- lexical-binding: t -*- to the header enables lexical binding in an elisp source file.

• inserting unicode by name

  C-x 8 RET lets you search and insert unicode character by Unicode name.

• getting mouse position

  There are functions to get current position of mouse both in terms of pixels mouse-pixel-position and characters mouse-position relative to current frame (or absolute mouse-absolute-pixel-position).

• smerge

  smerge-mode allows easy conflict resolution for merges. Move pointer to the conflict and use smerge-keep-mine / smerge-keep-other.

• edit file properties in dired

  Dired allows a special mode, wdired (C-x C-q), that lets dired buffer editings – like renaming files, changing permissions, etc. – get reflected to the file system. More details here.

• external functions in org tables

  Any babel code block returning value can be referenced by its name and called as a function for org tables. More details here.

• form feed lines

  Many popular elisp source files get rendered in spacemacs with sections separated by neat horizontal lines. TIL those are form feed characters ^L and are rendered using packages like page-break-lines.

• kill-ring

  Recently stopped using CUA keybindings. This opened me up to use the kill-ring, which is a list with kill (cut, copy) history. Simple cut, copy, paste are C-w (kill), M-w (kill-save) and C-y (yank). Cycle through the ring while yanking using M-y. Use helm-show-kill-ring for a better kill-ring browsing experience.

• elisp scripts

  Using Emacs for general purpose scripting has multiple issues. Many are documented here. For me, package loading is a major one. A lot of not-inside-emacs scripts wont be helpful without packages like f, dash and s. cask provides a way out. Init a caskfile (cask init), install dependencies (cask install), run (cask emacs --script something.el).

• data structures

  I never went beyond list. Knew about alists, but didn’t know there are hash tables and vectors too. In case you are working with key-value pairs in either hash table or alist form, try ht.el.

• org-contacts

  You can use org-contacts from org-contrib to manage contacts. This is really neat considering it integrates with gnus.

• mpc

  There is a pretty nifty mpd client built into Emacs. Use M-x mpc.