Windows Path Contract

Niubash uses a real Windows directory tree for its Unix-shaped shell paths. This is path spelling support, not MSYS, WSL, Cygwin, a POSIX runtime, or a filesystem overlay.

Ownership

Installation Root

For an installed executable such as:

C:/Users/Administrator/AppData/Local/Programs/Niubash/winuxcmd/usr/bin/winuxcmd.exe

the shell root is:

C:/Users/Administrator/AppData/Local/Programs/Niubash/winuxcmd/
  usr/bin/
  bin/
  usr/local/bin/
  etc/
  var/
  dev/
  .wpm/

These are ordinary Windows directories. usr/bin is canonical for winuxcmd.exe, wpm.exe, command links, and filename-only WPM targets. Explicit WPM targets under bin, usr/bin, or usr/local/bin remain in that exact directory. .wpm is private package state and is never a command path.

Niubash passes this exact root to Rubash as NIU_ROOT. Rubash maps paths lexically below it:

/             -> <root>
/usr/bin/tool -> <root>/usr/bin/tool
/bin/tool    -> <root>/bin/tool
/etc/config  -> <root>/etc/config

/tmp is deliberately NOT part of this tree: it is a per-user temporary namespace resolved to the real Windows temp directory (TMPDIR, else %TEMP%), so it stays writable under any install location (unixwin/niubash#94). /var/tmp resolves beside it as <real temp>/var/tmp. For every child that is not a bundled WinuxCmd applet, external command arguments are translated by the Rubash executor with the same rules — including /mnt/X drive spellings — so there is exactly one path-semantics owner and no host-side AST rewrite. Device spellings such as /dev/null are not part of that set; as arguments they reach the child verbatim. One child class is exempt from the drive-form rewrite, described under Shell Namespace Ownership.

Command lookup and native child PATH use these real directories directly. Rubash does not merge a second provider directory, and WinuxCmd coreutils do not inspect Niubash variables. Existing flat installations remain usable when their directory is explicitly present on PATH; new installs use the tree above.

Shell Namespace Ownership

A child process either resolves the shell namespace itself or receives native paths — never both, and never a guess about the child's capabilities:

• Bundled WinuxCmd applets own the shell tree (unixwin/niubash#346). The applets selected by the dispatcher route, the configured root, and the winuxcmd.exe tree marker receive /, /usr/bin, /etc, /tmp, /home, /mnt/X, the bare /, and /dev/* VERBATIM, and resolve them through WinuxCmd's own shell-tree layer, which mirrors Rubash's root map. They therefore render the POSIX face (ls -d /usr/bin, realpath /etc, readlink -f /tmp) and stay consistent with the spelling-preserving pwd. The executable-leaf convention is theirs too: /usr/bin/seq resolves to the real seq.exe while ls -d keeps the operand spelling, so head -1 /usr/bin/seq and test -f /usr/bin/seq agree (niubash#177).
• Every other child — a native Windows program, or a foreign POSIX runtime such as MSYS2 or Cygwin — receives native Windows paths. There is no per-child capability probe and no MSYS_NO_PATHCONV-style switch; a foreign runtime is treated exactly like a native program.
• One exception, and it is not a capability probe: cmd.exe. A single-letter drive form such as /d/repo or /c/Users reaches cmd.exe verbatim, because /d and /c are indistinguishable from cmd's own switches. Root forms and /mnt/X spellings are still translated, so cmd /c echo /usr/bin and cmd /c echo /mnt/c/Users arrive native while cmd /c echo /d/repo does not. The exemption is pinned in Rubash (is_windows_command_processor, and the windows_cmd_switches_are_not_mapped_into_shell_root test) and applies to cmd.exe alone: a native program that is not cmd receives /d/repo as D:\repo.

The boundary is structural rather than a rename of the "MSYS NO CONV" problem: the shell never asks a child what it can understand. The shipped toolchain's own resolution decides, and the engine compensates only for the child classes that cannot resolve the tree.

Dispatcher Selection

WINUXCMD_PATH selects one exact dispatcher executable for the session. Niubash resolves it, prepends that installation's usr/local/bin, usr/bin, and bin directories to the native PATH, and passes the exact executable to Rubash. Rubash does not discover another dispatcher from PATH.

The dispatcher is only a fallback when a command is absent from the real tree. It must not implement Rubash builtins such as cd, export, set, read, jobs, or trap.

Special Paths

~ is USERPROFILE, the same directory used by PowerShell. Windows paths such as C:/work/file and /c/work/file remain host paths.

The only device spelling currently supported is /dev/null. As a redirect target it is mapped to the native NUL endpoint; as an external-command argument it reaches the child verbatim, like the other /dev entries, which do not become ordinary files until their fd or terminal capability is implemented.