alex kuang

professional yak shaver

The Silver Searcher


This week I’d like to talk about grep. Grep is a great general-purpose tool and works very well for filtering text in the middle of a long command chain, but I’ve found it a bit clunky as a codebase search tool.

For example, let’s say you’re sitting in some project and trying to grep for all the places where a function is being called. The naïve first attempt would be:

grep myFunc

Except that just hangs, since grep defaults to reading from stdin. A next attempt might be:

grep myFunc .

Except then grep would complain that . is a directory, which leads to:

grep –r myFunc .

Which finally works, but still leaves a bit to be desired. The biggest annoyance is that grep will get caught up in files that you don’t necessarily care about, e.g. Tags files, third-party dependency files, binary files… “Binary file ./lib/default/xxx.jar matches” anyone?


Introducing ag, the silver searcher! Ag:

  • Fulfills the above “find this in cwd” use case via a simple, short ag myFunc
  • Is easy to install and super fast
  • Respects project ignore files: for example, it will ignore the patterns found in your .gitignore
  • In the case of files that you want in the repo but still don’t want to search, it also supports the use of a .agignore file
  • Integrates well into other tools: AFAIK there are ag plugins for vim, emacs, and text mate.

Fun fact: I was doing the whole grep –r thing for an embarrassingly long time before I bothered to search for a better workflow. My initial search turned up ack, which then led to ag. As far as I can tell, feature-wise they’re comparable; I eventually settled on ag just ‘cause the command requires less typing.