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Editorial Team
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Asked: 2026-06-06T07:25:56+00:00

My goal is to build a simple custom guard with Guard . The gem

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My goal is to build a simple custom guard with Guard. The gem install and bundler install for my app went fine. My Guardfile contains:

notification :growl

guard 'eyeball' do
  watch %r{^app/(.*)}
  watch %r{^config/(.*)}
  watch %r{^lib/(.*)}
end

Ok, next, I need to tell Guard what to do when a match happens. But I don’t know where to do that. (In this case, I want to watch my application for changes and run some arbitrary code. Assume that there isn’t a guard available for what I want. I want to learn how to do it myself.)

In true ‘blunder and see what errors pop up next’ style, when I run guard I get this error message:

ERROR: Could not load 'guard/eyeball' or find class Guard::Eyeball
ERROR: cannot load such file -- guard/eyeball
ERROR: Invalid Guardfile, original error is:
undefined method `new' for nil:NilClass
ERROR: No guards found in Guardfile, please add at least one.
Guard uses Growl to send notifications.
Guard is now watching at '/Users/my-user-name/dev/my-project-name'

So, that gives me a hint that I need to create a guard/eyeball.rb file. Maybe? But how was I supposed to know this from the documentation?

I’ve read (several times) the very detailed and useful Guard README but haven’t found a good simple example that shows someone how to do ‘just the basics’ of writing your own guard. Unexpectedly, RailsCasts didn’t really answer my question either: see RailsCast #264 Guard.

Did I overlook something in the Guard README? Can you help or point to a good example? Thanks!

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1 Answer

  1. Editorial Team

    Sweet! I just found a Wiki page on the Guard wiki titled Create a guard that answers my questions. It was not mentioned in the README, so I had to dig for it.

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