shell: do not wrap an escaped value in double quotes

[rawsun007]

---

• Have you followed our Contributing guidelines?
• Have you checked for other open Pull Requests for the same change?
• Have you explained what your changes do? Performance claims (e.g. "this is faster") must include brew benchmark results.
• Have you explained why you'd like these changes included, not just what they do?
• For bug fixes, have you given step-by-step brew commands to reproduce the bug?
• Have you written new tests (excluding integration tests)? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) locally?

---

• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

---

Utils::Shell.sh_quote backslash-escapes every character outside its safe set, which is the right escaping for a value that stands on its own. Three call sites wrapped that output in double quotes, where a backslash before an ordinary character stays literal:

$ brew ruby -e 'require "utils/shell"; puts Utils::Shell.export_value("HOMEBREW_FOO", "/opt/home brew", :bash)'
export HOMEBREW_FOO="/opt/home\ brew"

$ bash --norc -c 'export HOMEBREW_FOO="/opt/home\ brew"; printf "%s\n" "$HOMEBREW_FOO"'
/opt/home\ brew

The backslash lands in the value. set_variable_in_profile, in the same file, already emits export VAR=<escaped> with no quotes, so the file disagreed with itself about the same value.

Feeding 23 values (spaces, quotes, $, backticks, newlines, tabs, non-ASCII, empty) through the real shells and reading the variable back: 18 of 23 come back wrong under bash, zsh, sh and ksh, and 19 of 23 under fish. With the quotes removed, all 23 round-trip exactly in all five.

A default install never sees it, because /opt/homebrew and /usr/local contain nothing sh_quote escapes. It bites where a path does — a prefix with a space in it, or an SDK under an Xcode <version>.app, which reaches CMAKE_INCLUDE_PATH and HOMEBREW_SDKROOT. The callers are brew --env --shell=... and the keg-only build-flag caveats.

Two "supports Bash" examples and two --env examples asserted the quoted shape with values sh_quote does not touch, so all four changed; the three new examples use values that tell the two forms apart. Reverting only utils/shell.rb fails exactly those five shell examples and one --env example.

Deliberately untouched: prepend_path_in_profile and set_variable_in_profile wrap the line in echo '...', so a value containing a single quote still builds a malformed command. Different fix, no caller passes one today; happy to send it separately.

AI disclosure: written with Claude Code (Claude Opus 5) on my account. The counts above come from a harness that ran each generated line through the installed bash, zsh, sh, ksh and fish and compared the resulting variable against the input. I answer review comments myself.

[MikeMcQuaid]

Thanks!