The Silver Searcher: Better than Ack

A lot of my time spent “writing” code is actually spent reading code. And a decent chunk of my time spent reading code is actually spent searching code. Lately I’ve started working with a larger codebase.[1] Both grep and ack take a non-negligible amount of time to search it. Both are slow, but for different reasons. Grep is fast, but doesn’t ignore files.[2] Ack is very good at ignoring files, but it’s written in Perl instead of C. What I really want is something that’s fast and ignores files.

So I built it. I call it The Silver Searcher, or Ag) for short. Ag is like ack, but better. It’s fast. It’s damn fast. The only thing faster is stuff that builds indicies beforehand, like Exuberant Ctags.

Don’t believe me? Here are some benchmarks. I ran them multiple times and grabbed the median for each.

ggreer@carbon:~/cloudkick/reach% du -sh
250M    .

ggreer@carbon:~% time grep -r -i SOLR ~/cloudkick/reach | wc -l
     617
11.06s user 0.81s system 96% cpu 12.261 total

ggreer@carbon:~% time ack -i SOLR ~/cloudkick/reach | wc -l
     488
2.87s user 0.78s system 97% cpu 3.750 total

ggreer@carbon:~% time ag -i SOLR ~/cloudkick/reach | wc -l
     573
1.00s user 0.51s system 95% cpu 1.587 total

Here’s Ag with some extra ignores, similar to how ack ignores many files by default:

ggreer@carbon:~% cat ~/cloudkick/reach/.agignore 
extern
release
fixtures
ggreer@carbon:~% time ag -i SOLR ~/cloudkick/reach | wc -l
     499
0.35s user 0.15s system 94% cpu 0.528 total

That’s the same as git grep:

ggreer@carbon:~/cloudkick/reach% time git grep -i SOLR ~/cloudkick/reach | wc -l
     489
0.32s user 0.58s system 161% cpu 0.556 total

…except git grep only works in git repos. And it doesn’t ignore stuff in the repository like extern or generated files.[3]

The bottom line: Grep’s output was the least useful. It dutifully reported matches in .pyc files and other things I don’t care about. Ack’s results were better and faster than grep. Ag had more results than ack, but took half as long. With a couple of clever ignores (like the extern directory), Ag took a mere half-second and gave even more pertinent results.

I can already hear someone saying, “Big deal. It’s only a second faster. What does one second matter when searching an entire codebase?” My reply: trivial inconveniences matter. Using Ag is like having a faster computer; you don’t realize how slow things were until you’ve experienced fast. The difference is big enough that I can’t go back to ack, just like ack users can’t go back to grep.

Since it behaves like ack, Ag can be used by many fancy ack GUI front-ends. This makes searching convenient as well as fast. After I got Ag sorta-working, I forked AckMate so that I could use Ag in my favorite editor. My fork bundles both AckMate’s Ack and my own Ag. You can switch between them with a simple check box. The tmbundle is on the downloads page. Be warned: it replaces your current AckMate.

There’s still plenty of stuff I want to add,[4] but it’s good enough for my own daily use so I figured I should tell others about it. And of course, patches are welcome!


  1. The decision was made to put all python dependencies into extern/ instead of using pip. A good call, in my opinion.
  2. At least not without a bunch of pipes and find and xargs. Yes I know there are aliases but it’s annoying to keep those up-to-date.
  3. Yes, I know it’s bad form to put generated files in revision control.
  4. Ctags support, for one. Also inverted matching, accepting piped input, and basic stuff like retrying a search with fewer ignores and no case-sensitivity.


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