Add an opt-out for the built-in find→bfs / grep→ugrep shadow functions injected into the Bash tool shell

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/60325
2. https://github.com/anthropics/claude-code/issues/67623
3. https://github.com/anthropics/claude-code/issues/62642

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Not a duplicate. #60325 (broken ARGV0 dispatch → nested agent) and #67623 (mid-command shell kill + false ENOSPC banner) are closed crash bugs; #62642 is a bash<4.0 shell-termination crash. They report specific failures of the shadow mechanism.

This issue is a feature request for an opt-out toggle, motivated not by a crash but by semantic divergence between the embedded tools and their GNU counterparts:

• bfs parses leading-dash paths differently from GNU find, so find ./-somedir -name '*.x' fails (Unknown argument) where stock find works.
• ugrep's default --ignore-files makes a literal grep silently honor .gitignore — a different result set with no error.

A disable switch (env var or settings.json key) would be the umbrella mitigation: it makes every shadow-related failure above avoidable for users who just want stock find/grep semantics. Keeping this open as the consolidated opt-out request.

+1 for the opt-out. Adding a failure mode of the grep shadow we hit today that I have not seen reported elsewhere: process substitution silently returns empty.

Repro (macOS Darwin 25.5.0, zsh 5.9, Claude Code 2.1.212, inside the Bash tool):

grep -c x <(printf "x\nx\n")          # shadow/ugrep path -> NO output at all
command grep -c x <(printf "x\nx\n")  # -> 2 (correct)

No error message, no non-zero visible result — anything like n=$(grep -c … <(git show REV:file)) just yields an empty string, which then propagates through script logic unnoticed.

This compounds with the already-reported forced -G override (#59517) and the --ignore-files/-I default result-set differences. All of these share the same shape: silent divergence from GNU/BSD grep semantics in non-interactive/scripted use.

Until an opt-out exists, our workaround is a hard team rule: pipelines and script logic must use command grep / \grep; bare grep only for interactive human-read output.

Two measured consequences of the injected grep shadow (Claude Code 2.1.185, macOS, zsh snapshot), adding to the case for an opt-out:

1. -v exit-code semantics diverge from POSIX/GNU grep.

$ printf 'a\nb\n' | grep -qv a; echo $?
1        # shadow function (embedded ugrep): lines WERE selected, still exits 1
$ printf 'a\nb\n' | /usr/bin/grep -qv a; echo $?
0        # BSD/GNU: exits 0 when any line is selected

The same expression evaluated inside the Bash tool therefore returns the opposite answer locally vs. in CI (GNU grep). We caught this only because the expression gated a CI path-filter decision: an agent-authored grep -qvE-based check classified a mixed code+docs change as docs-only locally while behaving correctly on the runner. Related to #59517.

2. --ignore-files silently excludes gitignored files — secret sweeps report false-clean.

$ git init t && cd t && echo 'SECRET=1' > .env && echo '.env' > .gitignore
$ grep -rl SECRET .          # shadow: no matches
$ command grep -rl SECRET .  # ./.env

Agent-driven audits (leaked-credential sweeps, PII hunts, "is this string referenced anywhere" checks) run exactly this shape of command, and "no matches" reads as "clean". There is no indication in the output that gitignored files were skipped.

Both are silent-divergence failure modes rather than ergonomic ones: the shadow only affects the Bash tool's interactive shell (scripts run via bash script.sh don't inherit the function), which is precisely the unguarded ad-hoc layer.

Until an opt-out exists, the workaround we've adopted: command grep for anything judgment-bearing, plus a SessionStart hook that detects ARGV0=ugrep in the newest ~/.claude/shell-snapshots/snapshot-*.sh and warns the model at session start. +1 for CLAUDE_CODE_DISABLE_BUILTIN_SEARCH (or at minimum: don't pass --ignore-files when invoked under the name grep, and match POSIX exit semantics).