Adding an extra slash to --latest-npm gives an unclear error

[ferrybig]

• Operating system and version:

• nvm debug output:

nvm --version: v0.33.11
$SHELL: /bin/bash
$SHLVL: 2
$HOME: /home/fernando
$NVM_DIR: '$HOME/.nvm'
$PATH: $NVM_DIR/versions/node/v10.11.0/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
$PREFIX: ''
$NPM_CONFIG_PREFIX: ''
$NVM_NODEJS_ORG_MIRROR: ''
$NVM_IOJS_ORG_MIRROR: ''
shell version: 'GNU bash, version 4.4.19(1)-release (x86_64-pc-linux-gnu)'
uname -a: 'Linux 4.15.0-34-generic #37-Ubuntu SMP Mon Aug 27 15:21:48 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux'
OS version: Ubuntu 18.04.1 LTS  
curl: /usr/bin/curl, curl 7.58.0 (x86_64-pc-linux-gnu) libcurl/7.58.0 OpenSSL/1.1.0g zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1 (+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3
wget: /usr/bin/wget, GNU Wget 1.19.4 built on linux-gnu.
git: /usr/bin/git, git version 2.17.1
grep: /bin/grep (grep --color=auto), grep (GNU grep) 3.1
sed: -e expression #1, char 9: Unmatched ) or \)
awk: not an option: --version
awk: , 
sed: /bin/sed, sed (GNU sed) 4.4
cut: /usr/bin/cut, cut (GNU coreutils) 8.28
basename: /usr/bin/basename, basename (GNU coreutils) 8.28
rm: /bin/rm, rm (GNU coreutils) 8.28
mkdir: /bin/mkdir, mkdir (GNU coreutils) 8.28
xargs: /usr/bin/xargs, xargs (GNU findutils) 4.7.0-git
nvm current: v10.11.0
which node: $NVM_DIR/versions/node/v10.11.0/bin/node
which iojs: 
which npm: $NVM_DIR/versions/node/v10.11.0/bin/npm
npm config get prefix: $NVM_DIR/versions/node/v10.11.0
npm root -g: $NVM_DIR/versions/node/v10.11.0/lib/node_modules

• nvm ls output:

$ nvm ls
->     v10.11.0
         system
node -> stable (-> v10.11.0) (default)
stable -> 10.11 (-> v10.11.0) (default)
iojs -> N/A (default)
lts/* -> lts/carbon (-> N/A)
lts/argon -> v4.9.1 (-> N/A)
lts/boron -> v6.14.4 (-> N/A)
lts/carbon -> v8.12.0 (-> N/A)

• How did you install nvm? (e.g. install script in readme, Homebrew):
  script in readme: curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh | bash

• What steps did you perform?
  Ran accedentially nvm install ---latest-npm when trying to install the latest node version

• What happened?
  It gave weird & unclear errors:

grep: unrecognized option '---latest-npm'
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.
grep: unrecognized option '---latest-npm'
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.
Version '---latest-npm' not found - try `nvm ls-remote` to browse available versions.

• What did you expect to happen?

It should have given me a clear warning that I passed an unknown command flag to nvm, and not to grep

• Is there anything in any of your profile files (.bashrc, .bash_profile, .zshrc, etc) that modifies the PATH?
  I use the latest Ubuntu LTS version, and that one doesn't modify the path

[ljharb]

This is an interesting one. I'd expect here to send the arg to here where it's passed into here and so forth. I'll have to look into this.

[ljharb]

Considering that all unknown options to nvm install are assumed to be additional parameters passed to a source install, I'm not sure any error can be given here. The "fix" would be to make it not error at all.