Simple Shell Version Management: shenv

shenv lets you easily switch between multiple versions of shell. It's simple, unobtrusive, and follows the UNIX tradition of single-purpose tools that do one thing well.

This project was forked from pyenv (which itself is a fork of rbenv) and modified for the shell.

shenv does...

• Let you change the global shell version on a per-user basis.
• Provide support for per-project shell versions.
• Allow you to override the shell version with an environment variable.
• Search commands from multiple versions of shell at a time.

Table of Contents

• How It Works
  • Understanding PATH
  • Understanding Shims
  • Choosing the shell version
  • Locating the shell installation
• Installation
  • Basic GitHub Checkout
    • Upgrading
    • Advanced Configuration
    • Uninstalling shell versions
• Command Reference
• Development
• License

How It Works

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

Understanding PATH

When you run a command like bash or fish, 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

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

$(shenv root)/shims:/usr/local/bin:/usr/bin:/bin

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

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

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

Choosing the shell version

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

1. The SHENV_VERSION environment variable (if specified). You can use the shenv shell command to set this environment variable in your current shell session.

2. The application-specific .shell-version file in the current directory (if present). You can modify the current directory's .shell-version file with the shenv local command.

3. The first .shell-version file found (if any) by searching each parent directory, until reaching the root of your filesystem.

4. The global $(shenv root)/version file. You can modify this file using the shenv global command. If the global version file is not present, shenv assumes you want to use the "system" shell. (In other words, whatever version would run if shenv weren't in your PATH.)

Locating the shell installation

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

Each shell version is installed into its own directory under $(shenv root)/versions.

For example, you might have these versions installed:

• $(shenv root)/versions/2.7.8/
• $(shenv root)/versions/3.4.2/
• $(shenv root)/versions/pypy-2.4.0/

As far as shenv is concerned, version names are simply the directories in $(shenv root)/versions.

Managing Virtual Environments

There is a shenv plugin named shenv-virtualenv which comes with various features to help shenv users to manage virtual environments created by virtualenv or Anaconda. Because the activate script of those virtual environments are relying on mutating $PATH variable of user's interactive shell, it will intercept shenv's shim style command execution hooks. We'd recommend to install shenv-virtualenv as well if you have some plan to play with those virtual environments.

Installation

Basic GitHub Checkout

This will get you going with the latest version of shenv and make it easy to fork and contribute any changes back upstream.

1. Check out shenv where you want it installed. A good place to choose is $HOME/.shenv (but you can install it somewhere else).

    $ git clone https://github.com/shenv/shenv.git ~/.shenv
   

2. Define environment variable SHENV_ROOT to point to the path where shenv repo is cloned and add $SHENV_ROOT/bin to your $PATH for access to the shenv command-line utility.

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

   Zsh note: Modify your ~/.zshenv file instead of ~/.bash_profile.
   Ubuntu and Fedora note: Modify your ~/.bashrc file instead of ~/.bash_profile.
   Proxy note: If you use a proxy, export http_proxy and HTTPS_PROXY too.

3. Add shenv init to your shell to enable shims and autocompletion. Please make sure eval "$(shenv init -)" is placed toward the end of the shell configuration file since it manipulates PATH during the initialization.

   $ echo -e 'if command -v shenv 1>/dev/null 2>&1; then\n  eval "$(shenv init -)"\nfi' >> ~/.bash_profile

   Zsh note: Modify your ~/.zshenv file instead of ~/.bash_profile.
   Ubuntu and Fedora note: Modify your ~/.bashrc file instead of ~/.bash_profile.

   General warning: There are some systems where the BASH_ENV variable is configured to point to .bashrc. On such systems you should almost certainly put the abovementioned line eval "$(shenv init -)" into .bash_profile, and not into .bashrc. Otherwise you may observe strange behaviour, such as shenv getting into an infinite loop. See #264 for details.

4. Restart your shell so the path changes take effect. You can now begin using shenv.

   $ exec "$SHELL"

5. Install shell versions into $(shenv root)/versions. For example, to download and install Bash 4.4.12, run:

   $ shenv install bash-4.4.12

   NOTE: If you need to pass configure option to build, please use CONFIGURE_OPTS environment variable.

   NOTE: If you want to use proxy to download, please use http_proxy and https_proxy environment variable.

   NOTE: If you are having trouble installing a shell version, please visit the wiki page about Common Build Problems.

Upgrading

If you've installed shenv using the instructions above, you can upgrade your installation at any time using git.

To upgrade to the latest development version of shenv, use git pull:

$ cd $(shenv root)
$ git pull

To upgrade to a specific release of shenv, check out the corresponding tag:

$ cd $(shenv root)
$ git fetch
$ git tag
v0.1.0
$ git checkout v0.1.0

Uninstalling shenv

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

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

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

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

   rm -rf $(shenv root)

   If you've installed shenv using a package manager, as a final step perform the shenv package removal. For instance, for Homebrew:

    brew uninstall shenv
   

Advanced Configuration

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

shenv 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 shenv init actually does:

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

2. Installs autocompletion. This is entirely optional but pretty useful. Sourcing $(shenv root)/completions/shenv.bash will set that up. There is also a $(shenv root)/completions/shenv.zsh for Zsh users.

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

4. Installs the sh dispatcher. This bit is also optional, but allows shenv and plugins to change variables in your current shell, making commands like shenv 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 shenv to be a real script rather than a shell function, you can safely skip it.

To see exactly what happens under the hood for yourself, run shenv init -.

Uninstalling shell versions

As time goes on, you will accumulate shell versions in your $(shenv root)/versions directory.

To remove old shell versions, shenv uninstall command to automate the removal process.

Alternatively, simply rm -rf the directory of the version you want to remove. You can find the directory of a particular shell version with the shenv prefix command, e.g. shenv prefix 2.6.8.

Command Reference

See COMMANDS.md.

Environment variables

You can affect how shenv operates with the following settings:

Development

The shenv 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.

License

Software licensed under MIT license.