December 19, 2021

Clojure CLI - understanding aliases

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Clojure CLI provide a very flexible way to run Clojure and uses aliases in a deps.edn configuration file to optionally include execution options, code paths and library dependencies (Maven & Git). Aliases can be used with any of the Clojure CLI execution options that run with either clojure.main or clojure.exec.

Aliases provide a simple way to optionally include community libraries and tools for working with Clojure projects (e.g test runner, built tools, etc.). Community tools can be added to each Clojure project deps.edn configuration, or preferably to a user level deps.edn file for use with any Clojure project (easier to maintain as there is a central alias)

Understanding what an alias is and how to define them ensures an effective use of Clojure CLI and a smooth workflow.

Article updated 26th November 2022

practicalli/clojure-deps-edn a quick way to add many community tools on top of Clojure CLI tools. Practicalli also has tips for creating well designed aliases

The deps.edn configuration file

A deps.edn configuration file is a hash-map with several top level keywords. All the keywords are optional and the Clojure CLI install defines the src code path, org.clojure/clojure library dependency with Maven Central & as repository sources.

Configuration can be defined in a deps.edn file in the root of a Clojure project, applying only to that specific project.

A user level deps.edn configuration can be used in any Clojure project and the deps.edn configuration file resides in either $XDG_CONFIG_HOME/clojure or $HOME/.clojure.

What is an alias?

An alias is a way to add optional libraries, code paths or Clojure execution options (clojure.main, clojure.exec) when running Clojure CLI.

An alias name is a keyword in Clojure, e.g. :env/test, so the : is part of the alias name.

As aliases are optional, they provide a way to add libraries and tools that are only needed for development and testing of Clojure projects. For example, adding the test and dev directories to the Classpath, or test runners such as Kaocha.

The configuration keys that can be used to define an alias are:

  • :extra-paths - a vector of directory names added to the project class path, e.g. ["env/dev" "env/test"]
  • :extra-deps - a map of additional library dependencies, as a Maven library or Git repository
  • :main-opts - a vector of command line options passed to clojure.main
  • :exec-fn - the fully qualified name of a function to be run by clojure.exec
  • :exec-args - default arguments passed to the function, over-ridden by matching argument keys specified on the command line

:replace-paths and :replace-deps are used to only include specific directories and dependencies. excluding the project dependencies from the class path. Community tools that use these directives should consider adopting the tool -T flag approach.

Using :paths and :deps keys in an alias are short-hand for their replace-* keywords (Practicalli finds this very confusing, so prefers the explicit names for greater clarity)

A simple project deps.edn configuration

A new Clojure project can be made by creating a deps.edn file and respective src & test directory trees.

A project deps.edn file typically contains :path, :deps and :aliases sections, although deps.edn could start with a simple {} empty hash-map.

{:paths ["src" "resources"]
 {org.clojure/clojure {:mvn/version "1.11.1"}}
 {:env/test {:extra-paths ["test"]}}}

The test path and associated libraries are added as an alias as they are not required when packaging or running a Clojure application. :path and :deps keys are always included by default, :aliases are optional and only included when specified with the clojure command, e.g. clojure -M:env/test

Creating projects deps.edn from templates

clj-new provides a convenient way to create a project from a wide range of templates. deps-new is a newer project with a simpler template system to help create your own templates (although fewer community templates provided as yet).

The :project/new alias in practicalli/clojure-deps-edn configuration contains a configuration for clj-new.

In a terminal, create the project called practicalli/simple-api-server

clojure -X:project/new :template app :name practicalli/simple-api

This creates a Clojure namespace called simple-api in the practicalli domain. The project contains the clojure.core, test.check and test.runner libraries by default.

The deps.edn includes several aliases, some aliases have been adjusted and added from the template defaults to provide greater context.

{:paths ["src" "resources"]

 :deps {org.clojure/clojure {:mvn/version "1.10.3"}}

  {:main-opts ["-m" "practicalli.simple-api"]}

  {:exec-fn practicalli.simple-api-server/greet
   :exec-args {:name "Clojure"}}

  {:extra-paths ["test"]
   :extra-deps {org.clojure/test.check {:mvn/version "1.1.0"}}}

  {:extra-paths ["test"]
   :extra-deps {org.clojure/test.check {:mvn/version "1.1.1"}
                io.github.cognitect-labs/test-runner {:git/tag "v0.5.0" :git/sha "48c3c67"}}
   :main-opts ["-m" "cognitect.test-runner"]
   :exec-fn cognitect.test-runner.api/test}}}
  • project/run runs the Clojure project using clojure.main, so calls the -main function of the specified namespace
  • project/greet runs the fully qualified function greet (this could be any specified function in any of the project namespaces)
  • :env/test includes the test.check library and test code files under the test path, useful for REPL based test runners like CIDER.
  • :test/run sets the main namespace for the Cognitect Labs test runner, calling the -main function in that namespace that runs all the tests under the directory test. Also provides the :exec-fn for running with -X clojure.exec

:test/run alias shows an example of using a Git repository as a dependency. It uses the fully qualified repository name with a specific Git tag and commit :sha (any commit sha or tag in the history can be used). Clojure CLI tools will clone the repository when this alias is first used.

Update: the clj-new app template now uses the configuration to build and package a Clojure project.

Alias definition for clojure.main

:main-opts specifies the options passed to a clojure.main alias, using the clojure -M execution option flag.

The value is a vector containing individual string values that represent each option, i.e. option flag and value.

-m is used to define the fully qualified namespace in which clojure.main should look for the -main function.

The :main-opts vector defines arguments that are passed to the -main function, the same kind of arguments that would be passed via the command line.

The "--middleware" argument adds cider-nrepl middleware to the nREPL server, allowing Cider and other editors complete control over the REPL. The syntax uses values wrapped in a vector.

The "-interactive" argument runs an interactive REPL prompt. A headless process is run without this option.

  {:extra-deps {nrepl/nrepl                   {:mvn/version "0.9.0"}
                cider/cider-nrepl             {:mvn/version "0.27.4"}}
   :main-opts  ["-m" "nrepl.cmdline"
                "--middleware" "[cider.nrepl/cider-middleware]"

This alias is called using the command clojure -M:repl/cider

Alias definition for clojure.exec

:exec-fn specifies the fully qualified name of the function, using the clojure -X execution option flag .

:exec-args specifies a hash-map of default key/value pairs passed to the :exec-fn function. The defaults can be overridden on the command line with respective key/value pairs.

Arguments can be nested within the :exec-args map, especially useful on projects with several component configurations (server, database, logging) and managed by a component system (i.e Integrant)

  {:exec-fn practicalli.service/start
   :exec-args {:http/server {:port 8080
                             :join? fale}
               :log/mulog :elastic-search}}}}

To run with the default arguments:

clojure -X:project/run

Over-ride the default arguments by passing them on the command line

clojure -X:project/run '[:http/server :port]' 8888 :log/mulog :console :profile :dev

In this command the vector defines the path to the :port key and over-rides the default value. :log/mulog is a top-level key which changes the log publisher type. :profile is another top-level key that sets the environment to :dev (e.g. to configure Integrant / Aero).

Arguments in a nested map within the alias can be traversed (as with get-in and update-in functions) to override the default values in the alias. So to set a different port value :

Argument keys should either be a top-level key or a vector of keys to refer to a key in a nested hash-map of arguments.

An alias can contain configuration to run both clojure.main and clojure.exec (useful if steadily migrating users from -M to -X approach without breaking the user experience)

Form of clojure.exec command line arguments

Key/value pairs are read as EDN (extensible data notation that is the base syntax of Clojure).

The command line shell needs a little help parsing

Arguments that are vectors and hash maps should be wrapped in single quotes to avoid the command line shell splitting arguments at spaces, e.g. '[:a :b]', '{:c 1}'.

The double quotes in an EDN string must be wrapped by single quotes, along with vectors and hash-maps

Number values and keywords should not need to be wrapped.

  • '"strings in double quotes surround by single quotes"'
  • '[:kewords-are-okay :vectors-have-single-quotes]'
  • :config '{:so-do :hash-maps}'

User wide alias examples

practicalli/clojure-deps-edn contains numerous examples of user wide aliases that can be used across projects, especially common community tools.

The :test/watch alias adds Kaocha test runner in watch mode.

Using clojure -M:test/watch uses clojure.main to run Kaocha, passing in the :main-opts arguments.

Using clojure -X:test/watch uses clojure.exec to run the exec-fn function, passing the exec-args arguments.

  {:extra-paths ["test"]
   :extra-deps {lambdaisland/kaocha {:mvn/version "1.60.945"}}
   :main-opts   ["-m" "kaocha.runner" "--watch" "--no-randomize" "--fail-fast"]
   :exec-fn kaocha.runner/exec-fn
   :exec-args {:watch? true
               :randomize? false
               :fail-fast? true}}

NOTE: Configuration for both -M and -X approaches is not required, but both are often provided for convenience.

Community tools such as Kaocha have the opportunity to migrate to the -T tools approach. Read more about which execution option flag to use for Clojure CLI aliases

Further examples of aliases can be found in practicalli/clojure-deps-edn configuration which contains configurations for over 30 community tools.


You should have a better understanding of how to create aliases and what the individual keys in an alias configuration mean.

Practicalli also has tips for creating well designed aliases

See the next article in the series on using the most appropriate flags for Clojure CLI aliases

Thank you

Practicalli | @Practical_li

Tags: clojure-cli tools-deps