When I try to run the proposed script in my `~/.bashrc` file I get this output:
```
-bash: have: command not found
-bash: have: command not found
-bash: have: command not found
-bash: have: command not found
-bash: have: command not found
-bash: have: command not found
-bash: have: command not found
-bash: have: command not found
-bash: have: command not found
-bash: have: command not found
-bash: [: =: unary operator expected
# ...
```
It goes on for quite some time and does not give me bash completion.
When I execute `source "$(brew --prefix)/etc/bash_completion"` it works and I get bash completion.
This script also emits a helpful error message letting people know if bash completion was not installed already.
I'll also add that the bash completion script takes a fairly long amount of time. I've seen between one quarter and a half of a second to execute it:
```
$ time source "$(brew --prefix)/etc/bash_completion"
real 0m0.254s
```
Though that's unrelated to this PR, making a note of it.
