jlenv: Simple Julia Version Management

This project was forked from rbenv

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Use jlenv to pick a Julia version for your application and guarantee that your development environment matches production.

Powerful in development. Specify your app's Julia version once, in a single file. Keep all your teammates on the same page. No headaches running apps on different versions of Julia. Just Works™ from the command line and with app servers like Pow. Override the Julia version anytime: just set an environment variable.

Rock-solid in production. Your application's executables are its interface with ops. The Julia version dependency lives in one place—your app—so upgrades and rollbacks are atomic, even when you switch versions.

One thing well. jlenv is concerned solely with switching Julia versions. It's simple and predictable. A rich plugin ecosystem lets you tailor it to suit your needs. Compile your own Julia versions, or use the julia-build plugin to automate the process. See more plugins on the wiki.

Table of Contents

• How It Works
  • Understanding PATH
  • Understanding Shims
  • Choosing the Julia Version
  • Locating the Julia Installation
• Installation

• Basic GitHub Checkout
  • Upgrading with Git
• How jlenv hooks into your shell
• Installing Julia versions
  • Installing Julia gems
• Uninstalling Julia versions
• Uninstalling jlenv
• Command Reference
  • jlenv local
  • jlenv global
  • jlenv shell
  • jlenv versions
  • jlenv version
  • jlenv rehash
  • jlenv which
  • jlenv whence
• Environment variables
• Development

How It Works

At a high level, jlenv intercepts Julia commands using shim executables injected into your PATH, determines which Julia version has been specified by your application, and passes your commands along to the correct Julia installation.

Understanding PATH

When you run a command like julia, your operating system searches through a list of directories to find an executable file with that name. This list of directories lives in an environment variable called PATH, with each directory in the list separated by a colon:

/usr/local/bin:/usr/bin:/bin

Directories in PATH are searched from left to right, so a matching executable in a directory at the beginning of the list takes precedence over another one at the end. In this example, the /usr/local/bin directory will be searched first, then /usr/bin, then /bin.

Understanding Shims

jlenv works by inserting a directory of shims at the front of your PATH:

~/.jlenv/shims:/usr/local/bin:/usr/bin:/bin

Through a process called rehashing, jlenv maintains shims in that directory to match every Julia command across every installed version of Julia.

Shims are lightweight executables that simply pass your command along to jlenv. So with jlenv installed, when you run, say, julia, your operating system will do the following:

• Search your PATH for an executable file named julia
• Find the jlenv shim named julia at the beginning of your PATH
• Run the shim named julia, which in turn passes the command along to jlenv

Choosing the Julia Version

When you execute a shim, jlenv determines which Julia version to use by reading it from the following sources, in this order:

1. The JLENV_VERSION environment variable, if specified. You can use the jlenv shell command to set this environment variable in your current shell session.

2. The first .julia-version file found by searching the directory of the script you are executing and each of its parent directories until reaching the root of your filesystem.

3. The first .julia-version file found by searching the current working directory and each of its parent directories until reaching the root of your filesystem. You can modify the .julia-version file in the current working directory with the jlenv local command.

4. The global ~/.jlenv/version file. You can modify this file using the jlenv global command. If the global version file is not present, jlenv assumes you want to use the "system" Julia—i.e. whatever version would be run if jlenv weren't in your path.

Locating the Julia Installation

Once jlenv has determined which version of Julia your application has specified, it passes the command along to the corresponding Julia installation.

Each Julia version is installed into its own directory under ~/.jlenv/versions. For example, you might have these versions installed:

• ~/.jlenv/versions/v0.6.0/
• ~/.jlenv/versions/v0.6.0-rc3/
• ~/.jlenv/versions/v0.5.0/

Version names to jlenv are simply the names of the directories in ~/.jlenv/versions.

Installation

1. Install jlenv. Note that this also installs julia-build, so you'll be ready to install other Julia versions out of the box.

2. Run jlenv init and follow the instructions to set up jlenv integration with your shell. This is the step that will make running julia "see" the Julia version that you choose with jlenv.

3. Close your Terminal window and open a new one so your changes take effect.

4. That's it! Installing jlenv includes julia-build, so now you're ready to install some other Julia versions using jlenv install.

Basic GitHub Checkout

This will get you going with the latest version of jlenv without needing a systemwide install.

1. Clone jlenv into ~/.jlenv.

   $ git clone https://github.com/HiroakiMikami/jlenv.git ~/.jlenv

   Optionally, try to compile dynamic bash extension to speed up jlenv. Don't worry if it fails; jlenv will still work normally:

   $ cd ~/.jlenv && src/configure && make -C src
   

2. Add ~/.jlenv/bin to your $PATH for access to the jlenv command-line utility.

   $ echo 'export PATH="$HOME/.jlenv/bin:$PATH"' >> ~/.bash_profile

   Ubuntu Desktop note: Modify your ~/.bashrc instead of ~/.bash_profile.

   Zsh note: Modify your ~/.zshrc file instead of ~/.bash_profile.

3. Run ~/.jlenv/bin/jlenv init and follow the instructions to set up jlenv integration with your shell. This is the step that will make running julia "see" the Julia version that you choose with jlenv.

4. Restart your shell so that PATH changes take effect. (Opening a new terminal tab will usually do it.)

5. (Optional) Install julia-build, which provides the jlenv install command that simplifies the process of installing new Julia versions.

Upgrading with Git

If you've installed jlenv manually using Git, you can upgrade to the latest version by pulling from GitHub:

$ cd ~/.jlenv
$ git pull

How jlenv hooks into your shell

Skip this section unless you must know what every line in your shell profile is doing.

jlenv init is the only command that crosses the line of loading extra commands into your shell. Coming from RVM, some of you might be opposed to this idea. Here's what jlenv init actually does:

1. Sets up your shims path. This is the only requirement for jlenv to function properly. You can do this by hand by prepending ~/.jlenv/shims to your $PATH.

2. Installs autocompletion. This is entirely optional but pretty useful. Sourcing ~/.jlenv/completions/jlenv.bash will set that up. There is also a ~/.jlenv/completions/jlenv.zsh for Zsh users.

3. Rehashes shims. From time to time you'll need to rebuild your shim files. Doing this automatically makes sure everything is up to date. You can always run jlenv rehash manually.

4. Installs the sh dispatcher. This bit is also optional, but allows jlenv and plugins to change variables in your current shell, making commands like jlenv shell possible. The sh dispatcher doesn't do anything crazy like override cd or hack your shell prompt, but if for some reason you need jlenv to be a real script rather than a shell function, you can safely skip it.

Run jlenv init - for yourself to see exactly what happens under the hood.

Installing Julia versions

The jlenv install command doesn't ship with jlenv out of the box, but is provided by the julia-build project. If you installed it either as part of GitHub checkout process outlined above, you should be able to:

# list all available versions:
$ jlenv install -l

# install a Julia version:
$ jlenv install v0.6.0

Alternatively to the install command, you can download and compile Julia manually as a subdirectory of ~/.jlenv/versions/. An entry in that directory can also be a symlink to a Julia version installed elsewhere on the filesystem. jlenv doesn't care; it will simply treat any entry in the versions/ directory as a separate Julia version.

Uninstalling Julia versions

As time goes on, Julia versions you install will accumulate in your ~/.jlenv/versions directory.

To remove old Julia versions, simply rm -rf the directory of the version you want to remove. You can find the directory of a particular Julia version with the jlenv prefix command, e.g. jlenv prefix 1.8.7-p357.

The julia-build plugin provides an jlenv uninstall command to automate the removal process.

Uninstalling jlenv

The simplicity of jlenv makes it easy to temporarily disable it, or uninstall from the system.

1. To disable jlenv managing your Julia versions, simply remove the jlenv init line from your shell startup configuration. This will remove jlenv shims directory from PATH, and future invocations like julia will execute the system Julia version, as before jlenv.

jlenv will still be accessible on the command line, but your Julia apps won't be affected by version switching.

2. To completely uninstall jlenv, perform step (1) and then remove its root directory. This will delete all Julia versions that were installed under `jlenv root`/versions/ directory:

    rm -rf `jlenv root`
   

Command Reference

Like git, the jlenv command delegates to subcommands based on its first argument. The most common subcommands are:

jlenv local

Sets a local application-specific Julia version by writing the version name to a .julia-version file in the current directory. This version overrides the global version, and can be overridden itself by setting the JLENV_VERSION environment variable or with the jlenv shell command.

$ jlenv local v0.6.0

When run without a version number, jlenv local reports the currently configured local version. You can also unset the local version:

$ jlenv local --unset

jlenv global

Sets the global version of Julia to be used in all shells by writing the version name to the ~/.jlenv/version file. This version can be overridden by an application-specific .julia-version file, or by setting the JLENV_VERSION environment variable.

$ jlenv global v0.6.0

The special version name system tells jlenv to use the system Julia (detected by searching your $PATH).

When run without a version number, jlenv global reports the currently configured global version.

jlenv shell

Sets a shell-specific Julia version by setting the JLENV_VERSION environment variable in your shell. This version overrides application-specific versions and the global version.

$ jlenv shell v0.6.0

When run without a version number, jlenv shell reports the current value of JLENV_VERSION. You can also unset the shell version:

$ jlenv shell --unset

jlenv versions

Lists all Julia versions known to jlenv, and shows an asterisk next to the currently active version.

$ jlenv versions
  v0.6.0
* v0.6.0-rc1 (set by /Users/sam/.jlenv/version)

jlenv version

Displays the currently active Julia version, along with information on how it was set.

$ jlenv version
v0.6.0 (set by /Users/sam/.jlenv/version)

jlenv rehash

Installs shims for all Julia executables known to jlenv (i.e., ~/.jlenv/versions/*/bin/*). Run this command after you install a new version of Julia, or install a gem that provides commands.

$ jlenv rehash

jlenv which

Displays the full path to the executable that jlenv will invoke when you run the given command.

$ jlenv which julia
/Users/sam/.jlenv/versions/v0.6.0/bin/julia

jlenv whence

Lists all Julia versions with the given command installed.

$ jlenv whence julia
v0.6.0

Environment variables

You can affect how jlenv operates with the following settings:

name	default	description
JLENV_VERSION		Specifies the Julia version to be used. Also see jlenv shell
JLENV_ROOT	~/.jlenv	Defines the directory under which Julia versions and shims reside. Also see jlenv root
JLENV_DEBUG		Outputs debug information. Also as: jlenv --debug <subcommand>
JLENV_HOOK_PATH	see wiki	Colon-separated list of paths searched for jlenv hooks.
JLENV_DIR	$PWD	Directory to start searching for .julia-version files.

Development

The jlenv source code is hosted on GitHub. It's clean, modular, and easy to understand, even if you're not a shell hacker.

Tests are executed using Bats:

$ bats test
$ bats test/<file>.bats

Please feel free to submit pull requests and file bugs on the issue tracker.