I always seem to run into the constant problem of having to change multiple variables, symbols, function names, and other usually mundane parts of my code on a regular basis. Most likely due to the fact that I first name everything in a random, train of thought manner, only realising later that a more useful, explanatory definition is required.
Up until last night I found myself opening and closing multiple files after spending a few minutes in each finding and replacing keywords, and then ultimately running my code to find out I missed a few in this file, and a few in that file.
Take for example two files - one named foobar, and the other named foofoo. In both foobar and foofoo I have a something with the keywords foofunct. Now this something (variable, function, whatever) needs to have the same name in both these files. So I decided while editing the first file foobar that I want to change foofunct to foodef. With the change made to foobar lock in place and saved, I attempt to run my code, ultimately to be greeted by the wonderful world of errors saying something of the sort “your doing it wrong, I can’t find your flipping foofunct in foofoo anymore because it’s not in foobar”
Now this is an ongoing problem I’ve had and have always thought there has to be a better way…
Well maybe I'm just ignorant
Enter “The Silver Searcher” or “ag” for sort. Ag is a wonderful command line tool that lets you quickly search a code file, or set of files, to find a specific keyword within those file. Ag from the command line is awesome, but Ag in Emacs is amazing. By adding a few simple lines to my dotemacs file I am not able to find, replace, and view a single keyword across multiple files within a matter of seconds.
Adding some silver to your search (the code bit)
First you are going to have to make sure you have ag installed.
On Mac you can do this through homebrew very easily (if you don’t have homebrew installed already, join the future and install it)
Homebrew
$ brew install the_silver_searcherMacports
$ port install the_silver_searcherLinux (Debian/Ubuntu)
$ apt-get install silversearcher-ag
note: substitute apt-get for whichever package manager you use regularly
In your dotemacs
In your dotemacs you need a few things. (before you do anything use M-x package-install to get the required packages ag and wgrep (optional (projectile)) ;;it makes things a whole lot nicer
(when (executable-find "ag")
(require 'ag)
(require 'wgrep-ag)
(setq-default ag-highlight-search t)
(global-set-key (kbd "H-q") 'ag-project)
(global-set-key (kbd "H-z") 'projectile-ag)) ; if you have projectile
As you might noticed I am using Hyper-q H-q and Hyper-z H-z as hot keys for ag-*(whatever), you can change these to suit your preferred keybinding style.
A few other useful keybindings you may want to check out are C-x C-p, this makes the search buffer writable and lets you edit results inline. Also, C-c C-f, which activates next-error-follow-minor-mode, a nifty feature that quickly opens the file matching the search result your cursor is currently over.
The gif show at the top of this page is a demo of how I use it to navigate my emacs.d nightmare...here it is again so you don't have to scroll up to see it.
Silver Searching in Emacs
In (somewhat of a haphazard) Conclusion
With the setup complete you can now move you cursor over any variable, function name, definition, word, whatever and run ag on it to find all the uses of it in either a project, file, or if you’re feel ambitious your entire system (be warned, this sucks the life out of everything and may take a billion years to complete)