Repository: nvm
Issue: nvm install script fails to detect commented out nvm source string and bash_completion in ~/.bashrc
Labels: pull request wanted,installing nvm

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- Operating system and version:

macOS 10.13.6 (17G65)

- `nvm debug` output:
<details>
<!-- do not delete the following blank line -->

```sh
n/a
```
</details>

- `nvm ls` output:
<details>
<!-- do not delete the following blank line -->

```sh
n/a
```
</details>

- How did you install `nvm`? (e.g. install script in readme, Homebrew):

curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh | bash

- What steps did you perform?

1. `rm -rf $NVM_DIR`
1. `mkdir $NVM_DIR`
1. commented out the following 2 lines in .bashrc while debugging nvm 

    ```
    export NVM_DIR="$HOME/.nvm"
    # [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  # This loads nvm
    # [ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"  # This loads nvm bash_completion
    ```

1. (launch a new shell)
1. `curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh | bash`

- What happened?

`nvm` does not add the proper commands to .bashrc because it doesn't realize they are commented out.  Consequently, `nvm` also does not run since the script that loads it is never executed.

```
t-mbp:~ taylor$ curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh | bash
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 12819  100 12819    0     0  87888      0 --:--:-- --:--:-- --:--:-- 88406
=> Downloading nvm from git to '/Users/taylor/.nvm'
=> Cloning into '/Users/taylor/.nvm'...
remote: Counting objects: 267, done.
remote: Compressing objects: 100% (242/242), done.
remote: Total 267 (delta 31), reused 86 (delta 15), pack-reused 0
Receiving objects: 100% (267/267), 119.47 KiB | 1.81 MiB/s, done.
Resolving deltas: 100% (31/31), done.
=> Compressing and cleaning up git repository

=> nvm source string already in /Users/taylor/.bashrc
=> bash_completion source string already in /Users/taylor/.bashrc
env: node: No such file or directory
=> Close and reopen your terminal to start using nvm or run the following to use it now:

export NVM_DIR="$HOME/.nvm"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  # This loads nvm
[ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"  # This loads nvm bash_completion
t-mbp:~ taylor$ nvm
-bash: nvm: command not found
```

(Uncommenting these commands manually makes everything work as expected.)

- What did you expect to happen?

I expected `nvm` to detect that the commands are not actually in .bashrc (since they're commented out) and to add them.

Additionally, it would be nice to see a warning if the commands are there but commented out (i.e., further up in the .bashrc file from previous installs or troubleshooting).

- Is there anything in any of your profile files (`.bashrc`, `.bash_profile`, `.zshrc`, etc) that modifies the `PATH`?

Yes, I'm a developer so plenty of developer stuff but nothing else related to node / nvm besides the 3 lines added by nvm itself.