Aside on PR #10184

[RandomDSdevel]

Originally posted by @Rylan12 in Homebrew/brew#10184 (comment):

CI (on ubuntu-20.04) is now failing with the following message:

In /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/utils/ruby.sh line 20:
    for ruby_exec in $(which -a ruby 2>/dev/null) $(PATH=$HOMEBREW_PATH which -a ruby 2>/dev/null)
                       ^---^ SC2230: which is non-standard. Use builtin 'command -v' instead.
                                                                        ^---^ SC2230: which is non-standard. Use builtin 'command -v' instead.

For more information:
  https://www.shellcheck.net/wiki/SC2230 -- which is non-standard. Use builti...
Error: which is non-standard. Use builtin 'command -v' instead.

According to https://www.shellcheck.net/wiki/SC2230, this is opt-in only and I don't believe we've opted in... Odd that this is only the case on Ubuntu 20.04.

     I just wanted to note out-of-band that I've also seen this warning when running 'brew tests' while preparing recent PRs of my own for other things. Granted, the setup I've been limping along on is aaaaaaan-cient, at least in 'computer years,' and thus more than a bit of an outlier. (I'm still on OS X v10.11.6 'El Capitan,' build 15G22010, so feel free to ignore me; I just wanted to add another data point.)

[RandomDSdevel]

     For reference, my full 'brew config' as of right now (I haven't run 'brew update yet today) is:

…~ …$ brew config
HOMEBREW_VERSION: 2.7.1
ORIGIN: https://github.com/Homebrew/brew.git
HEAD: fdb71a5cb3029da2ef74d7e09c40575bbfb4ec72
Last commit: 3 days ago
Core tap ORIGIN: https://github.com/Homebrew/homebrew-core
Core tap HEAD: 963d33f8193d0a1537a8dada41fa7938085325ec
Core tap last commit: 15 hours ago
Core tap branch: master
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CASK_OPTS: ["--appdir=/Applications", "--prefpanedir=/Library/PreferencePanes", "--colorpickerdir=/Library/ColorPickers", "--dictionarydir=/Library/Dictionaries", "--servicedir=/Library/Services", "--qlplugindir=/Library/QuickLook", "--fontdir=/Library/Fonts", "--input_methoddir=/Library/Input Methods", "--screen_saverdir=/Library/Screen Savers", "--internet_plugindir=/Library/Internet Plug-Ins"]
HOMEBREW_DISPLAY: /private/tmp/com.apple.launchd.lcUd9snI2W/org.macosforge.xquartz:0
HOMEBREW_EDITOR: nano --fill=100
HOMEBREW_FORCE_BREWED_CURL: set
HOMEBREW_FORCE_BREWED_GIT: set
HOMEBREW_GITHUB_API_TOKEN: set
HOMEBREW_MAKE_JOBS: 2
HOMEBREW_NO_AUTO_UPDATE: set
HOMEBREW_UPDATE_TO_TAG: set
Homebrew Ruby: 2.6.3 => /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.3_2/bin/ruby
CPU: dual-core 64-bit core2
Clang: 8.0 build 800
Git: 2.20.1 => /usr/local/opt/git/bin/git
Curl: 7.63.0 => /usr/local/opt/curl/bin/curl
Java: 11.0.2
macOS: 10.11.6-x86_64
CLT: 8.2.0.0.1.1480973914
Xcode: 8.2.1
XQuartz: 2.7.11 => /opt/X11

(Yes, I'm aware my Java installation is out of date. That doesn't matter in this context, though.)

[Rylan12]

Okay, I finally got around to troubleshooting this. Turns out the issue is that the version of shellcheck was too old.

You need to use a version of shellcheck that's either < 0.5.0 or >= 0.7.1. My recommendation is to use the most recent version of shellcheck (which happens to be 0.7.1).

For more info see Homebrew/brew#10192 (comment)

So, to solve your problem, you should just need to update shellcheck to the latest version.

Interestingly, though, I didn't see this issue when running brew tests...