Copying gems from previous version of Ruby in rbenv - ruby

Question

I installed Ruby 1.9.3-p286 with rbenv. Now, after installing a newer version (p327), obviously, it doesn't know anything about the GEMs installed with the previous version.
Is it possible to copy Gems from that version to the newer one, so that it won't be needed to download them all again?

Answer 1

You can copy the gems/ and bin/ folders, but this will lead to problems. The files in bin/ have hardcoded paths in them.
I'd recommend reinstalling them, which would be as easy as this:
$ rbenv local 1.9.3-p286
$ gem list | cut -d" " -f1 > my-gems
$ rbenv local 1.9.3-p327
$ gem install $(cat my-gems)

Answer 2

I've been looking at this specifically from the perspective of upgrading and reinstalling without downloading. It's not trivial, and I recommend you do some cleanup of your gems to minimize the amount of processing/installation that needs to be done (e.g., I had five versions of ZenTest installed; I did 'gem cleanup ZenTest' before doing this). Be careful with 'gem cleanup', though, as it removes all but the LAST version: if you need to support an older version of Rails, manually clean up the versions you don't need.
I called this script 'migrate-gems.sh':
#! /bin/bash
if [ ${#} -ne 2 ]; then
echo >&2 Usage: $(basename ${0}) old-version new-version
exit 1
fi
home_path=$(cd ~; pwd -P)
old_version=${1}
new_version=${2}
rbenv shell ${old_version}
declare -a old_gem_paths old_gems
old_gem_paths=($(gem env gempath | sed -e 's/:/ /'))
rbenv shell ${new_version}
for ogp in "${old_gem_paths[#]}"; do
case "${ogp}" in
${home_path}/.gem/ruby*|*/.gem/ruby*)
# Skip ~/.gem/ruby.
continue
;;
esac
for old_gem in $(ls -1 ${ogp}/cache/*.gem); do
gem install --local --ignore-dependencies ${ogp}/cache/${old_gem}
done
done
There are three pieces that make this work:
gem env gempath contains the paths (:-separated) where gems are installed. Because
gems are shared in ~/.gem/ruby, I skip this one.
gem install accepts --local, which forces no network connections.
gem install accepts --ignore-dependencies, which disables dependency checking.
I had a fairly large list of gems to move over today and I didn't want to download from rubygems.org (plus, I needed older versions), so I whipped this up fairly quickly.

Answer 3

For posterity, I wrote rbenv-copy-gems.sh to help me do this. It doesn't meet the criteria of this question (it installs from the Internet, not locally), but it's been useful for me as I upgrade or install new version of Ruby via rbenv install.
Current version pasted below for reference, but I keep the gist up to date as I make improvements.
#!/bin/bash
# copy is a misnomer; it's actually LIST + INSTALL
# --from 2.2.1 [--to other-version-else-whatever-is-currently-set]
#
# TODO: install only most-recent version that's installed in FROM
# TODO: use gem names only from FROM, install latest available version (might be more recent than in FROM)
# TODO: pass arguments to gem command (e.g. --no-document)
CURRENT_VERSION=`rbenv version | cut -d' ' -f1`
GEM_LIST_ARGS="--local"
while [[ $# -gt 0 ]]; do
option="$1"
case $option in
--from)
FROM="$2"
shift
;;
--to)
TO="$2"
shift
;;
esac
shift # past argument or value
done
if [ -z "${FROM}" ]; then
FROM="${CURRENT_VERSION}"
fi
if [ -z "${TO}" ]; then
TO="${CURRENT_VERSION}"
fi
echo ">>> Install gems from v${FROM} to v${TO}"
# Get gems and versions, reformat to GEMNAME:version[,version[...]]
gems=(`RBENV_VERSION=${FROM} gem list ${GEM_LIST_ARGS} | sed -e 's/[\(\)]//g' -e 's/, /,/g' -e 's/ /:/'`)
for geminfo in "${gems[#]}"; do
gem=`echo $geminfo | cut -d: -f1`
versions=(`echo $geminfo | sed -e 's/^.*://' -e 's/,/ /g'`)
for version in "${versions[#]}"; do
installed=`RBENV_VERSION=${TO} gem query -i $gem -v $version`
if [ "${installed}" == "false" ]; then
echo ">>> Installing ${gem} ${version}:"
RBENV_VERSION=${TO} gem install $gem -v $version
else
echo ">>> ${gem} ${version} already installed"
fi
echo ""
done
done