Authoring plugins

Jason Karns edited this page Dec 27, 2015 · 3 revisions

rbenv plugins provide new commands and/or hook into existing functionality of rbenv. The following file naming scheme should be followed in a plugin project:

  1. bin/rbenv-COMMAND for commands
  2. etc/rbenv.d/HOOK_NAME/*.bash for hooks

rbenv commands

An rbenv command is an executable named like rbenv-COMMAND. It will get executed when a user runs rbenv COMMAND. Its help will be displayed when a user runs rbenv help COMMAND. It can be written in any interpreted language, but bash script is recommended for portability.

A plugin command can't override any of the rbenv's built-in commands.

Environment

Each rbenv command runs with the following environment:

  • $RBENV_ROOT - where rbenv versions & user data is placed, typically ~/.rbenv
  • $RBENV_DIR - the current directory of the caller
  • $PATH - constructed to contain:
    1. rbenv's libexec dir with core commands
    2. $RBENV_ROOT/plugins/*/bin for plugin commands
    3. $PATH (external value)

Calling other commands

When calling other commands from a command, use the rbenv-COMMAND form (with dash) instead of rbenv COMMAND (with space).

Use rbenv's core low-level commands to inspect the environment instead of doing it manually. For example, read the result of rbenv-prefix instead of constructing it like $RBENV_ROOT/versions/$version.

A plugin command shouldn't have too much knowledge of rbenv's internals.

Help text

An rbenv command should provide help text in the topmost comment of its source code. The help format is described in rbenv help help.

Here is a template for an executable called rbenv-COMMAND:

#!/usr/bin/env bash
#
# Summary: One line, short description of a command
#
# Usage: rbenv COMMAND [--optional-flag] <required-argument>
#
# More thorough help text wrapped at 70 characters that spans
# multiple lines until the end of the comment block.

set -e
[ -n "$RBENV_DEBUG" ] && set -x

# Optional: Abort with usage line when called with invalid arguments
# (replace COMMAND with the name of this command)
if [ -z "$1" ]; then
  rbenv-help --usage COMMAND >&2
  exit 1
fi

Completions

A command can optionally provide tab-completions in the shell by outputting completion values when invoked with the --complete flag.

# Provide rbenv completions
if [ "$1" = "--complete" ]; then
  echo hello
  exit
fi

Note: it's important to keep the above comment intact. This is how rbenv detects if a command is capable of providing completion values.

rbenv hooks

Hooks are bash scripts named like HOOK_NAME/*.bash, where "HOOK_NAME" is one of:

  • exec
  • rehash
  • version-name
  • version-origin
  • which

Hooks are looked for in $RBENV_HOOK_PATH, which is composed of:

  1. $RBENV_HOOK_PATH (external value)
  2. $RBENV_ROOT/rbenv.d
  3. /usr/local/etc/rbenv.d
  4. /etc/rbenv.d
  5. /usr/lib/rbenv/hooks
  6. $RBENV_ROOT/plugins/*/etc/rbenv.d

Hook scripts are executed at specific points during rbenv operation. They provide a low-level entry point for integration with rbenv's functionality. To get a better understanding of the possibilities with hooks, read the source code of rbenv's hook-enabled commands listed above.