DEP(1) -- basic dependency tracking

SYNOPSIS

dep check
dep add libname [--pre]
dep rm libname
dep install

DESCRIPTION

• check: Checks that all dependencies are met.

• add: Fetches the latest version of the library in question and automatically adds it to your .gems file.

• rm: Simply removes the corresponding entry in your .gems file.

• install: Installs all the missing dependencies for you. An important point here is that it simply does a gem install for each dependency you have. Dep assumes that you use some form of sandboxing like gs, RVM or rbenv-gemset.

INSTALLATION

$ gem install dep

HISTORY

dep is actually more of a workflow than a tool. If you think about package managers and the problem of dependencies, you can summarize what you absolutely need from them in just two points:

1. When you build an application which relies on 3rd party libraries, it's best to explicitly declare the version numbers of these libraries.
2. You can either bundle the specific library version together with your application, or you can have a list of versions.

The first approach is handled by vendoring the library. The second approach typically is done using Bundler. But why do you need such a complicated tool when all you need is simply listing version numbers?

We dissected what we were doing and eventually reached the following workflow:

1. We maintain a .gems file for every application which lists the libraries and the version numbers.
2. We omit dependencies of dependencies in that file, the reason being is that that should already be handled by the package manager (typically rubygems).
3. Whenever we add a new library, we add the latest version.
4. When we pull the latest changes, we want to be able to rapidly check if the dependencies we have is up to date and matches what we just pulled.

So after doing this workflow manually for a while, we decided to build the simplest tool to aid us with our workflow.

• The first point is handled implicitly by dep. You can also specify a different file by doing dep -f.
• The second point is more of an implementation detail. We thought about doing dependencies, but then, why re-implement something that's already done for you by rubygems?
• The third point (and also the one which is most inconvenient), is handled by dep add.

The manual workflow for dep add would be:

gem search -r "^ohm$" [--pre] # check and remember the version number
echo "ohm -v X.x.x" >> .gems

If you try doing that repeatedly, it will quickly become cumbersome.

The fourth and final point is handled by typing dep check or simply dep. Practically speaking it's just:

git pull
dep

And that's it. The dep command typically happens in 0.2 seconds which is something we LOVE.