docs/Shell-Completion: read both types of bash completions.

[MikeMcQuaid]

And guard against either of them being missing.

Fixes #5610

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

[ikatza]

Hey for whatever reason the first if doesn't evaluate to true on my case:

if type brew 2&>/dev/null; then echo "inside"; fi prints nothing.

Doing:

if type brew &>/dev/null; then echo "inside"; fi yields
inside

echo $BASH_VERSION
5.0.2(1)-release

and also tried on Linux with bash version 4.2.+.

[MikeMcQuaid]

@ikatza What does which brew output on your system?

[ikatza]

$ which brew
/usr/local/bin/brew

$ type brew
brew is /usr/local/bin/brew

[MikeMcQuaid]

@ikatza You'll need to figure this out yourself, then, that all looks like it should work.

[ikatza]

Well that's kinda of what I did.

I've been googling for the 2&> redirection idiom, but can't find that specific combination.
I found the &> idiom that redirects STDOUT and STDERR.

$ if type brew &>/dev/null; then echo "inside"; fi
inside
 
$ if type brewwww &>/dev/null; then echo "inside"; fi

[maxim-belkin]

2&> is not a valid redirection instruction in Bash.
You don't need to google stuff that you can find with man bash:

   Redirecting Standard Output and Standard Error
       This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be  redi-
       rected to the file whose name is the expansion of word.

       There are two formats for redirecting standard output and standard error:

              &>word
       and
              >&word

       Of the two forms, the first is preferred.  This is semantically equivalent to

              >word 2>&1

       When using the second form, word may not expand to a number or -.  If it does, other redirection operators apply (see Duplicating
       File Descriptors below) for compatibility reasons.

[maxim-belkin]

Oh! There is a typo in instructions!

[maxim-belkin]

this is the typo

[MikeMcQuaid]

I also misread that typo, my apologies @ikatza. Opened a PR in #5781

[raldred]

I get masses of errors when using this snippet in my bashrc

-bash: have: command not found
-bash: /usr/local/etc/bash_completion.d/ant: line 45: syntax error in conditional expression: unexpected token `('
-bash: /usr/local/etc/bash_completion.d/ant: line 45: syntax error near `-@(?'
-bash: /usr/local/etc/bash_completion.d/ant: line 45: `            if [[ "${COMP_WORDS[i]}" == -@(?(build)file|f) ]]; then'
-bash: have: command not found
-bash: /usr/local/etc/bash_completion.d/apt: line 12: syntax error in conditional expression: unexpected token `('
....[clipped]

Full output here: https://gist.github.com/raldred/098801f9ea47bd37c64652af2ef35baf

[maxim-belkin]

This means you have bash-completion installed and your Bash is newer. Uninstall bash-completion.