Fast Loading for `nvm` and SDKMAN!

July 21, 2021

Some time ago I was trying to make bash start faster. There, I described a solution to load nvm and SDKMAN! faster. However, that solution has a few issues.

we always need to call one of nvm, node, or npm before we can call any other node.js-related command
we can avoid the previous problem by manually adding them to 50-nvm.bashrc, but this is error-prone and cumbersome
when we add a new utility, we need to manually add them to the list, and to every function there
if we switch the default node.js version, then we need to re-evaluate the whole script. for example, our node.js 12 installation has yarn installed, but our node.js 14 installation doesn't have it installed. we would then need to remove yarn from the bashrc script

To solve this, we need something that:

can automatically find the currently-used node version
can autogenerate the list and the functions, according to which utilities are installed

The solution

After some thinking and experimentation, I have come up with a new solution:

.bashrc.d/50-nvm.bashrc
_DEFAULT=
# read the first line only
[ -s "${HOME}/.nvm/alias/default" ] && read -r _DEFAULT <"${HOME}/.nvm/alias/default"

if [ -n "${_DEFAULT}" ]; then
  # this will simplify the checks below
  _DEFAULT=${_DEFAULT#v}
  _DEFAULT=${_DEFAULT%.}

  if [ -d "${HOME}/.nvm/versions/node/v${_DEFAULT}/bin" ]; then
    _DEFAULT_DIR="${HOME}/.nvm/versions/node/v${_DEFAULT}/bin"
  elif [ -d "${HOME}/.nvm/versions/node/v${_DEFAULT}".*/bin ]; then
    _DEFAULT_DIR="$(echo "${HOME}/.nvm/versions/node/v${_DEFAULT}".*/bin)"
  else
    _DEFAULT_DIR=
  fi

  _NVM_BIN_LIST=
  if [ -n "${_DEFAULT_DIR}" ]; then
    for _EXEC in "${_DEFAULT_DIR}"/*; do
      if [ -x "${_EXEC}" ]; then
        _CMD="${_EXEC##*/}"
        eval "${_CMD}"'() { _nvm_load; '"${_CMD}"' "$@"; }'
        _NVM_BIN_LIST="${_NVM_BIN_LIST} ${_CMD}"
      fi
    done
  fi
fi

_CMD='nvm'
eval "${_CMD}"'() { _nvm_load; '"${_CMD}"' "$@"; }'

eval '_nvm_load() {
  unset -f _nvm_load nvm '"${_NVM_BIN_LIST}"'
  export NVM_DIR="${HOME}/.nvm"
  [ -s "${NVM_DIR}/nvm.sh" ] && . "${NVM_DIR}/nvm.sh"
  [ -s "${NVM_DIR}/bash_completion" ] && . "${NVM_DIR}/bash_completion"
}'

unset _CMD _NVM_BIN_LIST _EXEC _DEFAULT_DIR _DEFAULT

When the script is sourced in by .bashrc, it will first try to read the default version. This is usually read in as something like 12 or 12.22. With that version information, it tries to find the corresponding nvm directory and list all the executables there. For each executable, a placeholder shell function is created. When we first call the placeholder, it will initialize nvm, after which everything will return to normal.

This is the environment on my laptop:

william@william-ThinkPad-T450s: ~$ cat .nvm/alias/default
12
william@william-ThinkPad-T450s: ~$ ls -l .nvm/versions/node/v12*/bin/*
-rwxr-xr-x 1 william william 48928552 Apr  6 22:06 .nvm/versions/node/v12.22.1/bin/node
lrwxrwxrwx 1 william william       42 May 17 13:12 .nvm/versions/node/v12.22.1/bin/nodemon -> ../lib/node_modules/nodemon/bin/nodemon.js
lrwxrwxrwx 1 william william       38 Jun 21 01:34 .nvm/versions/node/v12.22.1/bin/npm -> ../lib/node_modules/npm/bin/npm-cli.js
lrwxrwxrwx 1 william william       38 Jun 21 01:34 .nvm/versions/node/v12.22.1/bin/npx -> ../lib/node_modules/npm/bin/npx-cli.js
lrwxrwxrwx 1 william william       36 Jun 10 22:51 .nvm/versions/node/v12.22.1/bin/yarn -> ../lib/node_modules/yarn/bin/yarn.js
lrwxrwxrwx 1 william william       36 Jun 10 22:51 .nvm/versions/node/v12.22.1/bin/yarnpkg -> ../lib/node_modules/yarn/bin/yarn.js
lrwxrwxrwx 1 william william       33 May 27 20:20 .nvm/versions/node/v12.22.1/bin/yo -> ../lib/node_modules/yo/lib/cli.js
lrwxrwxrwx 1 william william       46 May 27 20:20 .nvm/versions/node/v12.22.1/bin/yo-complete -> ../lib/node_modules/yo/lib/completion/index.js
william@william-ThinkPad-T450s: ~$ type _nvm_load nvm node npm yarn
_nvm_load is a function
_nvm_load () 
{ 
    unset -f _nvm_load nvm node nodemon npm npx yarn yarnpkg yo yo-complete;
    export NVM_DIR="${HOME}/.nvm";
    [ -s "${NVM_DIR}/nvm.sh" ] && . "${NVM_DIR}/nvm.sh";
    [ -s "${NVM_DIR}/bash_completion" ] && . "${NVM_DIR}/bash_completion"
}
nvm is a function
nvm () 
{ 
    _nvm_load;
    nvm "$@"
}
node is a function
node () 
{ 
    _nvm_load;
    node "$@"
}
npm is a function
npm () 
{ 
    _nvm_load;
    npm "$@"
}
yarn is a function
yarn () 
{ 
    _nvm_load;
    yarn "$@"
}

The placeholder function for yo is there, I just didn't show it.

Loading time

Loading time is still fast enough:

$ time . .bashrc.d/50-nvm.bashrc 

real    0m0.002s
user    0m0.001s
sys 0m0.001s

Testing

With this loading script, nvm still functions correctly:

$ yarn --version
1.22.10

$ node --version
v12.22.1

$ nvm --version
0.38.0

$ npm --version
7.18.1

Also, it still respects .nvmrc as described here:

william@william-ThinkPad-T450s: ~$ mkdir test
william@william-ThinkPad-T450s: ~$ echo 14 >test/.nvmrc
william@william-ThinkPad-T450s: ~$ mkdir test/foo
william@william-ThinkPad-T450s: ~$ cd test/foo
william@william-ThinkPad-T450s: ~/test/foo$ nvm use
Found '/home/william/test/.nvmrc' with version <14>
Now using node v14.17.1 (npm v7.19.0)
william@william-ThinkPad-T450s: ~/test/foo$ cd ..
william@william-ThinkPad-T450s: ~/test$ nvm use
Found '/home/william/test/.nvmrc' with version <14>
Now using node v14.17.1 (npm v7.19.0)
william@william-ThinkPad-T450s: ~/test$ cd ..
william@william-ThinkPad-T450s: ~$ nvm use
No .nvmrc file found
Please see `nvm --help` or https://github.com/nvm-sh/nvm#nvmrc for more information.

Shortcomings

Of course, no solution is perfect. Otherwise the nvm developers would have adopted it as their official solution/workaround to the slow loading times of nvm. However, there is currently one way that I can think of, to make this solution fail: install a new utility in another terminal session.

In this scenario, we first open a terminal window, but don't call any nvm or node.js-related command. Let's say we don't have yarn installed at this point. Then in another terminal window, we install yarn. Now, in the first terminal window, we cannot execute yarn without first calling nvm or any other existing commands.

The reverse is not a problem. Let's say we have yo installed. If we uninstall yo in the other terminal window, when we try to execute it in the first terminal window, it will just fail. This is the exact same behaviour as a vanilla nvm installation.

Please let me know if you have any other potential pitfalls and shortcomings

What about SDKMAN! ?

Well, SDKMAN! is a bit simpler than nvm:

.bashrc.d/50-sdkman.bashrc
_SDK_BIN_LIST=
for _EXEC in "${HOME}/.sdkman/candidates"/*/current/bin/*; do
  if [ -x "${_EXEC}" ]; then
    _CMD="${_EXEC##*/}"
    eval "${_CMD}"'() { _sdk_load; '"${_CMD}"' "$@"; }'
    _SDK_BIN_LIST="${_SDK_BIN_LIST} ${_CMD}"
  fi
done

_CMD='sdk'
eval "${_CMD}"'() { _sdk_load; '"${_CMD}"' "$@"; }'

eval '_sdk_load() {
  unset -f _sdk_load sdk '"${_SDK_BIN_LIST}"'
  export SDKMAN_DIR="${HOME}/.sdkman"
  [ -s "${SDKMAN_DIR}/bin/sdkman-init.sh" ] && . "${SDKMAN_DIR}/bin/sdkman-init.sh"
}'

unset _CMD _SDK_BIN_LIST _EXEC

Since SDKMAN! uses a current symlink for each installed candidate, we can just use this. No need to manually figure out the currently-used version.

The solution for SDKMAN! suffers the same shortcoming as the one for nvm, so please also let me know if you find something wrong with it.

The solution​

Loading time​

Testing​

Shortcomings​

What about SDKMAN! ?​

The solution

Loading time

Testing

Shortcomings

What about SDKMAN! ?