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Michael Klishin f1b1d05430
Merge pull request #655 from hugoduncan/feature/plugin-fix-for-lein2-project-location
11 years ago
bin Fix for trampoline command parsing on Windows. 11 years ago
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resources Move "deploy" help to "deploying" to avoid collision. 12 years ago
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"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.

Leiningen logo

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.

  1. Download the script.
  2. Place it on your path. (I like to use ~/bin)
  3. 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 downloads page. 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 search ... # find recent jars for your project.clj dependencies

Use 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 (new, help, version, plugin, and the two-argument version of install) may run from anywhere.

The install task places shell scripts in the ~/.lein/bin directory for projects that include them, so if you want to take advantage of this, you should put it on your $PATH.


The project.clj file in the project root should look like this:

(defproject myproject "0.5.0-SNAPSHOT"
  :description "A project for doing things."
  :url ""
  :dependencies [[org.clojure/clojure "1.2.1"]
                 [org.clojure/clojure-contrib "1.2.0"]]
  :dev-dependencies [[lein-ring "0.4.5"]])

If you're looking for the most recent jar of one of your dependencies, use lein search.

The lein new task generates a project skeleton with an appropriate starting point from which you can work. See the sample.project.clj file for a detailed listing of configuration options.

You can also have user-level configuration that applies for all projects. The ~/.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.

Leiningen Plugins

Leiningen supports plugins. See the plugins wiki page for a full list. If a plugin is needed for successful test or build runs, (such as lein-tar) then it should be added to :dev-dependencies in project.clj, but if it's for your own convenience (such as swank-clojure) then it should be added using the plugin task:

$ 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: 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, and the copy in checkouts will take precedence over the dependency declared in project.clj. Note that this is not a replacement for listing the project in :dependencies; it simply supplements that for convenience. You can run lein classpath to see how the addition of the checkouts affects the project's classpath.

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.<init>(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 upon it.

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 Maven guide.

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 swank-clojure or 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.

It is possible to use a 32-bit JVM for the lein process while using a 64-bit JVM for sub-processes such as swank-clojure, by setting the environment variable LEIN_JAVA_CMD to the path of your 32-bit java binary and the JAVA_CMD env variable to the path of the 64-bit version.

Q: I don't have access to stdin inside my project.
A: This is a limitation of the JVM's process-handling methods; none of them expose stdin correctly. 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 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 a 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 run lein-stable deps in your checkout. If Leiningen's dependencies change it will be necessary to remove the lib/ directory entirely before running lein deps again. (This is not necessary for most projects, but Leiningen has unique bootstrapping issues when working on itself.)

You can also use Maven, just for variety's sake:

$ mvn dependency:copy-dependencies
$ mv target/dependency lib

Symlink 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.