Command substitution in brew.env?

[dkav]

Output of brew config

HOMEBREW_VERSION: 4.1.12-8-gafbea15
ORIGIN: https://github.com/Homebrew/brew
HEAD: afbea15d5cc2129b03498ebcc5e96dc5641c8874
Last commit: 8 hours ago
Core tap origin: https://github.com/Homebrew/homebrew-core
Core tap HEAD: 350287d04fec605d86f58f2f382e1a8c778ced27
Core tap last commit: 2 hours ago
Core tap branch: master
Core tap JSON: 25 Aug 18:13 UTC
HOMEBREW_PREFIX: /usr/local
HOMEBREW_AUTOREMOVE: set
HOMEBREW_BROWSER: open
HOMEBREW_CASK_OPTS: []
HOMEBREW_CLEANUP_MAX_AGE_DAYS: 14
HOMEBREW_DEVELOPER: set
HOMEBREW_EDITOR: /usr/local/bin/mvim
HOMEBREW_GITHUB_API_TOKEN: set
HOMEBREW_MAKE_JOBS: 8
HOMEBREW_NO_EMOJI: set
HOMEBREW_NO_ENV_HINTS: set
HOMEBREW_NO_INSTALL_FROM_API: set
HOMEBREW_NO_UPDATE_REPORT_NEW: set
HOMEBREW_SORBET_RUNTIME: set
Homebrew Ruby: 2.6.10 => /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.10_1/bin/ruby
CPU: octa-core 64-bit ivybridge
Clang: 12.0.0 build 1200
Git: 2.42.0 => /usr/local/bin/git
Curl: 7.64.1 => /usr/bin/curl
macOS: 10.15.7-x86_64
CLT: 12.0.0.32.29
Xcode: N/A

Output of brew doctor

Your system is ready to brew.

Description of issue

Is there a way to replicate export HOMEBREW_GITHUB_API_TOKEN=$( cat ~/.token/homebrew_github_api_token ) that I have in my shell profile in the new environment files (brew.env). I tried but the command substitution does not occur–as seen from the error Error: GitHub API Error: Bad credentials and the debug output\%\{http_code\} --header Authorization:\ token\ \$\(\ cat\ \~/.token/homebrew_github_api_token\ \). Using the raw token in brew.env worked fine.

[dkav]

Substitution is not supported in brew.env, see #16027 for more details.