"Leiningen!" he shouted. "You're insane! They're not creatures you can fight--they're an elemental--an 'act of God!' Ten miles long, two miles wide--ants, nothing but ants! And every single one of them a fiend from hell..." -- from Leiningen Versus the Ants by Carl Stephenson
Leiningen is for automating Clojure projects without setting your hair on fire.
Working on Clojure projects with tools designed for Java can be an exercise in frustration. With Leiningen, you just write Clojure.
Leiningen bootstraps itself using the
lein shell script;
there is no separate install script. It installs its dependencies
upon the first run on unix, so the first run will take longer.
- Download the script.
- Place it on your path. (I like to use
- Set it to be executable. (
chmod 755 ~/bin/lein)
On Windows most users can get
the batch file.
If you have wget.exe or curl.exe already installed and in PATH, you
can just run
lein self-install, otherwise get the standalone jar from the
If you have Cygwin you should be able to use
the shell script above rather than the batch file.
The tutorial has a detailed walk-through of the steps involved in creating a new project, but here are the commonly-used tasks:
$ lein new NAME # generate a new project skeleton $ lein test [TESTS] # run the tests in the TESTS namespaces, or all tests $ lein repl # launch an interactive REPL session and socket server $ lein jar # package up the whole project as a .jar file $ lein install [NAME VERSION] # install a project
lein help to see a complete list.
lein help $TASK shows the
usage for a specific one.
You can also chain tasks together in a single command by using commas:
$ lein clean, test foo.test-core, jar
Most tasks need to be run from somewhere inside a project directory to
work, but some (
plugin, and the
two-argument version of
install) may run from anywhere.
The install task places shell scripts in the
directory for projects that include them, so if you want to take
advantage of this, you should put it on your
project.clj file in the project root should look like this:
(defproject myproject "0.5.0-SNAPSHOT" :description "A project for doing things." :url "http://github.com/technomancy/myproject" :dependencies [[org.clojure/clojure "1.2.1"] [org.clojure/clojure-contrib "1.2.0"]] :dev-dependencies [[lein-ring "0.4.5"]])
lein new task generates a project skeleton with an
appropriate starting point from which you can work. See the
file for a detailed listing of configuration options.
You can also have user-level configuration that applies for all
~/.lein/init.clj file will be loaded every time
Leiningen launches; any arbitrary code may go there. This code is
executed inside Leiningen itself, not in your project. Set the
:repl-init key in project.clj to point to a namespace if
you want code executed inside your project.
You can also manage your plugins with the
plugin task. Use
the same arguments you would put in the Leiningen :dev-dependencies if
you were only using the plugin on a single project.
$ lein plugin install lein-clojars "0.6.0"
See the plugin task's help for more information.
$ lein plugin help
Q: How do you pronounce Leiningen?
A: It's LINE-ing-en. ['laɪnɪŋən]
Q: What does this offer over Lancet?
A: Lancet is more of a library than a build tool. It doesn't predefine any tasks apart from what Ant itself offers, so there is nothing Clojure-specific in it. Leiningen builds on Lancet, but takes things further. In addition, it includes some Maven functionality for dependencies.
Q: But Maven is terrifying!
A: That's not a question. Anyway, Leiningen only uses the dependency resolution parts of Maven, which are quite tame. For some other build-related functionality it uses Ant under the covers via Lancet.
Q: But Ant is terrifying!
A: That's true. Ant is an interpreter for a procedural language with a regrettable syntax. But if you treat it as a standard library of build-related functions and are able to write it with a more pleasing syntax, it's not bad.
Q: What's a group ID? How do snapshots work?
A: See the tutorial for background.
Q: How should I pick my version numbers?
A: Use semantic versioning.
Q: It says a required artifact is missing for "super-pom". What's that?
A: The Maven API that Leiningen uses refers to your project as "super-pom". It's just a quirk of the API. It probably means there is a typo in your :dependency declaration in project.clj.
Q: What if my project depends on jars that aren't in any repository?
A: The deploy guide explains how to set up a private repository. If you are not sharing them with a team you could also just install locally..
Q: How do I write my own tasks?
A: If it's a task that may be useful to more than just your project, you should make it into a plugin. You can also include one-off tasks in your src/leiningen/ directory if they're not worth spinning off; the plugin guide shows how.
Q: I want to hack two projects in parallel, but it's annoying to switch between them.
A: Use a feature called checkout dependencies. If you create a directory called
checkouts in your project root and symlink
some other project roots into it, Leiningen will allow you to hack
on them in parallel. That means changes in the dependency will be
visible in the main project without having to go through the whole
install/switch-projects/deps/restart-repl cycle. Note that this is
not a replacement for listing the project in :dependencies; it
simply supplements that for tighter change cycles.
Q: Is it possible to exclude indirect dependencies?
A: Yes. Some libraries, such as log4j, depend on projects that are not included in public repositories and unnecessary for basic functionality. Projects listed as :dependencies may exclude any of their dependencies by using the :exclusions key. See sample.project.clj for details.
Q: What does java.lang.NoSuchMethodError: clojure.lang.RestFn.(I)V mean?
A: It means you have some code that was AOT (ahead-of-time) compiled with a different version of Clojure than the one you're currently using. If it persists after running
lein clean then it
is a problem with your dependencies. Note that for
your own project that AOT compilation in Clojure is much less
important than it is in other languages. There are a few
language-level features that must be AOT-compiled to work, generally
for Java interop. If you are not using any of these features, you
should not AOT-compile your project if other projects may depend
Q: I'm behind an HTTP proxy; how can I fetch my dependencies?
A: Currently you need to configure the underlying Maven library by creating
~/.m2/settings.xml as explained in the
Q: What can be done to speed up launch?
A: The main delay involved in Leiningen comes from starting the JVM. Launching
lein interactive will give you an interactive
session so you can run many tasks against the same process instead
of launching a new one every time. Depending on your editor you may
also be able to take advantage of its Clojure integration. (See
VimClojure, for example.)
Q: Still too slow; what else can make startup faster?
A: There are two flavours of the JVM, client and server. The server is optimized for long-running processes and has quite a poor startup time. Leiningen will try to launch a client JVM, but this only works on 32-bit JVM installations. If you are on a 64-bit machine you can still use a client JVM if you install 32-bit packages; on Debian try ia32-sun-java6-bin. Once you've installed it, run
sudo update-java-alternatives -s ia32-java-6-sun.
Q: I don't have access to stdin inside my project.
A: There's a bug in the Ant library that Leiningen uses to spawn new processes that blocks access to console input. This means that functions like
read-line will not work as expected in most
contexts, though the
repl task necessarily includes a
workaround. You can also use the
trampoline task to
launch your project's JVM after Leiningen's has exited rather than
launching it as a subprocess
Please report issues on the Github issue tracker or the mailing list. Personal email addresses are not appropriate for bug reports. See the file HACKING.md for more details on how Leiningen's codebase is structured.
You don't need to "build" Leiningen per se, but when you're using a
checkout you will need to get its dependencies in place. In most cases
lein self-install will usually get you what you
need. However, this will occasionally fail for very new SNAPSHOT
versions since the standalone jar will not have been uploaded yet.
Alternatively if you have a copy of an older Leiningen version around
(at least 1.1.0, installed as lein-stable, for example), then you can
lein-stable deps in your checkout. If Leiningen's dependencies
change it will be necessary to remove the lib/ directory entirely
lein deps again. (This is not necessary for most
projects, but Leiningen has unique bootstrapping issues when working
You can also use Maven, just for variety's sake:
$ mvn dependency:copy-dependencies $ mv target/dependency lib
bin/lein from your checkout into a location on the $PATH. The
script can figure out when it's being called from inside a checkout
and use the checkout rather than the self-install uberjar if necessary.
Copyright © 2009-2011 Phil Hagelberg, Alex Osborne, Dan Larkin, and other contributors.
Thanks to Stuart Halloway for Lancet and Tim Dysinger for convincing me that good builds are important.
Distributed under the Eclipse Public License, the same as Clojure uses. See the file COPYING.