pyenv/libexec/rbenv-prefix

#!/usr/bin/env bash
# Summary: Display prefix for a Ruby version
# Usage: rbenv prefix [<version>]
#
# Displays the directory where a Ruby version is installed. If no version is
# given, it uses the currently selected version.

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

# Provide rbenv completions
if [ "$1" = "--complete" ]; then
  echo system
  exec rbenv-versions --bare
fi

if [ -n "$1" ]; then
  export RBENV_VERSION="$1"
elif [ -z "$RBENV_VERSION" ]; then
  RBENV_VERSION="$(rbenv-version-name)"
fi

if [ "$RBENV_VERSION" = "system" ]; then
  RUBY_PATH="$(rbenv-which ruby)"
  RUBY_PATH="${RUBY_PATH%/*}"
  echo "${RUBY_PATH%/bin}"
  exit
fi

RBENV_PREFIX_PATH="${RBENV_ROOT}/versions/${RBENV_VERSION}"
if [ ! -d "$RBENV_PREFIX_PATH" ]; then
  echo "rbenv: version \`${RBENV_VERSION}' not installed" >&2
  exit 1
fi

echo "$RBENV_PREFIX_PATH"