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…hell=bun run without a system shell With HOME unset, the Bun shell expanded "~" to "" so "~/x" became "/x". Move the getpwuid_r lookup from os.homedir() into bun_sys::os::passwd_home_dir and use it as the fallback for "~". "cd" with no argument still reports "HOME not set". "bun run" resolved the system shell before it checked --shell=bun, so an image without /bin/sh failed with "An internal error occurred (MissingShell)" even when the built-in shell was requested. Look the system shell up only when it is used, and give MissingShell a message.
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| Layer / File(s) | Summary |
|---|---|
Home-directory lookup API src/sys/os.rs, src/sys/lib.rs, src/runtime/node/node_os.rs |
bun_sys::os::passwd_home_dir() performs the Unix passwd lookup. Node’s homedir uses the shared function and maps its results to home-directory values or errors. |
Shell home resolution and tilde expansion src/runtime/shell/interpreter.rs, src/runtime/shell/states/Expansion.rs, test/js/bun/shell/bunshell.test.ts |
Shell home lookup checks shell_env before export_env and uses platform fallbacks or a Unix passwd home as applicable. Tilde expansion uses an available home path or preserves a literal ~; tests cover these outcomes. |
Possibly related PRs
- oven-sh/bun#42599: Both changes use environment and passwd sources for home-directory behavior.
- oven-sh/bun#46687: Both changes modify leading-tilde processing in
Expansion.
Suggested reviewers: alii, jarred-sumner, dylan-conway
Priority:
Merge Risk: 
b7d11
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The previously reported missing-home expansion issue is fixed. No remaining issue identified here prevents merging after normal checks.
Pre-merge checks: 
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Check name Status Explanation Title check The title clearly and concisely identifies the main change: using the passwd home for tilde expansion when HOME is unset. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request. Description check The description is complete and relevant. It explains the problem, implementation, behavior changes, limitations, and verification steps. It does not use the template headings exactly, but it provides… Full details: Description check
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Explanation
The description is complete and relevant. It explains the problem, implementation, behavior changes, limitations, and verification steps. It does not use the template headings exactly, but it provides the required information, including how the code was verified.
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Updated 12:29 AM PT - Oct 29th, 2026
❌ @robobun, your commit dbdedb6 has 9 failures in
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CapacityLimitExceededThis account has reached its capacity limit. Reach out to your account team for assistance.79f9a888-ed82-45cc-b75e-7c4a00c814ef🧪 To try this PR locally: bunx bun-pr 43202That installs a local version of the PR into your bun-43202 --bun |
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Status The branch now includes
Reproduced on a debug build of Two new tests in The |
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…-shell=bun without a shell With no $HOME and no usable passwd entry, "~" expanded to "". Keep the "~" instead. Android keeps /data/local/tmp for both "~" and "cd": bionic synthesizes a passwd entry with "/" or "/data" for every uid. "cd" is back to the code on main. Add a test for "bun run --shell=bun" on a system with no shell. A seccomp user-notification helper answers ENOENT for every path the shell lookup probes.
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Inline comments:
In `@src/runtime/shell/states/Expansion.rs`:
- Around line 238-239: Update the None branch in the tilde expansion logic to
append home_bytes when either has_quoted_empty is true or no home value was
found (home.is_none()). Preserve the existing empty-word behavior while ensuring
an unquoted suffix such as ~&`#36`;UNSET retains the literal tilde instead of
being omitted.
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src/crash_handler/lib.rssrc/runtime/cli/run_command.rssrc/runtime/node/node_os.rssrc/runtime/shell/interpreter.rssrc/runtime/shell/states/Expansion.rssrc/sys/lib.rssrc/sys/os.rstest/cli/run/hide-paths.ctest/cli/run/run-shell.test.tstest/js/bun/shell/bunshell.test.ts
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It shares no file with the ~ fix. It is now #43231.
robobun
changed the title
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I re-reviewed the PR after the last push moved the --shell=bun half out and found no bugs in what remains; a human look is still worthwhile because this changes user-visible ~ semantics in the shell (including Windows, where ~ with USERPROFILE unset now stays literal), and the title/description still describe the run_command.rs / MissingShell / run-shell.test.ts work that is no longer in this diff.
What was reviewed:
EnvStrrefcount balance at both tilde sites:EnvMap::getandinit_ref_countedeach hand back +1, and bothExpansion.rssitesderef()only onSome, so no leak or double-free.passwd_home_dirbuffer lifetime:pw_diris read after the loop breaks,heapis only reassigned before a retry, so the SAFETY claim holds;node_os.rspreserves the Android default, non-Android ENOENT on null result, and empty string on nullpw_dir.- Tests: the first test fails on base (
echo ~ a ~/xgivesa /x); the root-only uid test follows the existinguid:-drop pattern inno-orphans.test.ts/fs.watch.test.tsandbunEnvis the file-local definition.
Extended reasoning...
Overview
The diff now covers six files: a new bun_sys::os::passwd_home_dir() (src/sys/os.rs, registered in src/sys/lib.rs) that hosts the getpwuid_r retry loop previously inline in src/runtime/node/node_os.rs; node_os.rs homedir rewritten to call it; ShellExecEnv in src/runtime/shell/interpreter.rs split into home_env(), get_homedir() (for cd, behaviour unchanged) and get_tilde_home() (env, then Android default, then passwd on unix, else None); both tilde sites in src/runtime/shell/states/Expansion.rs now emit a literal ~ when no home is known; and two new tests in test/js/bun/shell/bunshell.test.ts. The last commit (1abec63b) removed the run_command.rs, crash_handler, hide-paths.c and run-shell.test.ts changes, so the PR title and description are now broader than the code.
Security risks
None new. The passwd lookup runs as the effective uid against the local NSS database; the only externally influenced input is pw_dir, which is copied out of the buffer as bytes and never interpreted as a path by this code. The unbounded doubling on repeated ERANGE was raised on an earlier push and is unchanged from the pre-existing node_os.rs loop, so it is not a regression introduced here.
Level of scrutiny
Moderate. The Rust is small and I traced the refcount and buffer lifetimes directly: EnvMap::get calls ref_(), RefCountedStr::init starts at 1, and both Expansion.rs sites deref() exactly once on Some. home_bytes borrows the Option<EnvStr> (which is Copy) and is not used after the match, so the borrow ends before deref. On Windows src/sys/os.rs compiles down to a doc comment, and get_tilde_home keeps EnvStr in use through the cfg!(IS_ANDROID) arm, so the use is not dead. What warrants a human is the semantic choice: ~ now stays literal on Windows when USERPROFILE is unset (previously ""), which is stated in the description but only tested on POSIX, and the ~$unset-with-known-home behaviour is intentionally left as before.
Other factors
Three prior review rounds from this system exist; every earlier inline thread was resolved by the author, and the last push materially changed scope, so a fresh note is warranted rather than silence. The first new test demonstrably fails on base. The root-only test depends on the debug binary and cwd being readable by an arbitrary uid, which existing tests (no-orphans.test.ts, fs.watch.test.ts) already assume in CI. Not approving because the change alters user-facing shell semantics across platforms and the PR text no longer matches the diff.
Conflict in test/js/bun/shell/bunshell.test.ts: each side added a name to the "fs" import. The merge keeps both.
…other uids cannot reach The first test no longer needs the runner's uid to have a passwd entry: the child catches the os.homedir() error, and the test then expects a literal ~. The root-only test gives its child cwd "/" and skips when the other uid cannot traverse to the bun binary.
There was a problem hiding this comment.
The latest push addresses both test concerns from the previous round, and this automated review found no bugs in the current revision; since it changes user-visible ~ semantics in the Bun shell and adds a new unsafe bun_sys helper, a human look is still worthwhile.
What was reviewed:
passwd_home_dirvs the old inline loop innode_os.rs: errno mapping, nullpw_dir-> EMPTY, Android default and non-Android ENOENT are preserved;pw_diris copied out of the local buffer before return.get_tilde_home/ bothExpansion.rssites: theinit_ref_countedEnvStr is deref'd exactly once on each path,init_slicevalues are not, andHOME=""still expands to the empty string (the existing test covers it);cdkeepsget_homedirwith the old fallback.- Windows/Android cfg shape:
src/sys/os.rsis fully#[cfg(unix)]so the unconditionalpub mod osyields an empty module there, andget_tilde_homefalls through toNoneon Windows. - New tests: the child now catches
os.homedir()ENOENT and expects a literal~, the root-only test usescwd: "/"and skips when another uid cannot traverse tobunExe(), and pipes are drained withPromise.all.
Extended reasoning...
The change moves the getpwuid_r loop from src/runtime/node/node_os.rs into a new src/sys/os.rs helper, adds ShellExecEnv::get_tilde_home in src/runtime/shell/interpreter.rs, switches both tilde sites in src/runtime/shell/states/Expansion.rs to it so ~ with HOME unset uses the passwd home or stays literal, and adds two subprocess tests in test/js/bun/shell/bunshell.test.ts. It touches no auth, crypto or injection surface; the sensitive part is unsafe FFI into getpwuid_r and the shell's EnvStr refcounting, both of which check out. Commit b7d112b resolved the two inline test findings posted on the prior revision and no new issues were found, but the PR alters user-facing shell semantics and the author notes the helper duplicates one in another open PR, so a maintainer should still weigh the design rather than this being auto-approved.
Problem
HOMEunset, the Bun shell expands~to the empty string.echo ~/xprints/x, andrm -rf ~/.cachetargets/.cache. bash andos.homedir()use the passwd entry.ShellExecEnv::get_homedir(src/runtime/shell/interpreter.rs:2030), which defaults to"".Fix
~now reads$HOME, then the passwd entry. With neither, the~stays.cdand Android are not changed.getpwuid_rloop moves fromos.homedir()intobun_sys::os::passwd_home_dir(). The newget_tilde_homecalls it for both expansion sites instates/Expansion.rs.bun run --shell=bunchange is now bun run: do not look for a system shell when --shell=bun runs the script #43231). Kept: the helper copies node:os, CompressionStream, TextEncoder/TextDecoder: remove unsafe #40244 on purpose.test/js/bun/shell/bunshell.test.ts. Both fail without the fix (a /x). Alsoos.test.js,cargo checkfor Windows, macOS, Android.Background
Bun.$andbun run --shell=bun.states/Expansion.rsexpands a word's~.os.homedir()follows libuv:$HOME, elsegetpwuid_r(geteuid()). The shell only had the first half.$HOMEfrom the passwd entry at shell start:echo $HOMEandcdwould then differ from bash. Considered a literal~always, as in dash: bash andos.homedir()use the passwd entry.Downsides
HOMEunset now gets<passwd home>/xfor~/x, not/x. On Windows withUSERPROFILEunset,~stays~.HOMEunset, each~word costs onegetpwuid_rcall, which opens/etc/passwd(measured: 10 words, 10 opens). Nothing is cached. WithHOMEset there is no new work.os.homedir()withHOMEunset allocates one more copy of the path.Notes
~withHOMEunset, before and after (env -u HOME bun -e ..., uid 0):POSIX leaves
~withHOMEunset unspecified. bash uses the passwd entry and dash keeps the~. Neither gives the empty string. The Bun shell follows bash when there is a passwd entry, which also matchesos.homedir()in the same process, and keeps the~when there is none (no entry, an emptypw_dir, or a lookup error). The first new test holds for any runner uid: with a passwd entry it expects<home> a <home>/x, without one it expects~ a ~/x. The second new test needs root: it runs the child as a uid that has no passwd entry, withcwd/, runsecho ~ a ~/x ~"" ~$UNSET_VARIABLE, and expects~ a ~/x ~ ~. It skips when that uid cannot reach the bun binary. The released binary printsa /xthere. With a known home,~$unsetis still dropped as before.HOMEis unset underenv -i, in a systemd unit withoutUser=, and in some container runtimes.cdwithHOMEunset still printsHOME not set, as bash does.HOME=""still expands to the empty string, as in bash. The existing test "empty $HOME or $USERPROFILE" covers it. On Windows,~withUSERPROFILEunset now stays~and no longer becomes"".Android: bionic synthesizes a passwd entry with
/or/datafor every uid, so~andcdkeep the/data/local/tmpdefault from main and do not read the passwd entry.Cost of the lookup, counted with a seccomp user-notification tracer that logs every path syscall of the child.
HOMEunset:echo ~opens/etc/passwd1 time,echowith 10~words 10 times,echo x0 times.HOMEset, 10~words: 0 times. Threeos.homedir()calls withHOMEunset: 3 opens, the same as before this change.bun_sys::os::passwd_home_dirhas the same module path, name, signature and logic as the helper that open PR #40244 adds. If #40244 lands first, take itssrc/sys/os.rs. The callers here compile against it unchanged.The
bun run --shell=bunchange that was part of this PR is now #43231. It shares no file with this fix.no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/shell/bunshell.test.ts