repo_shape.py, setup-project.py, shape-doctor.py, README and the handbook: under Git Bash (MSYSTEM set) the lines that follow the host are quoted for sh, through one question, host_shell_dialect, so the doctor's lines, setup's family lines and family.py's NEXT, switch -c, add and cd lines paste whole in the shell that printed them, and README's Windows sentence says so

README.md

@@ -157,10 +157,12 @@ Windows way in that installs nothing; pipx's `openRepoShape` runs the same flow.
 Git Bash runs step 3's bash command and its one line, tested in CI but for a
 typed `yes`, which its preflight cannot take there. Printed commands are quoted
 for a POSIX shell, so paste them into Git Bash. Only `shape-doctor.py`'s lines,
-`setup-project.py`'s family lines and `family.py`'s `NEXT`, `switch -c`, `add`
-and `git rm -r --cached` lines are quoted for PowerShell, on Windows.
-Off Windows, a path `shape-doctor.py` cannot print as itself is written `$'…'`:
-bash, zsh and ksh read that; dash (`/bin/sh` on Debian and Ubuntu) does not.
+`setup-project.py`'s family lines and `family.py`'s `NEXT`, `switch -c`, `add`,
+`cd` and `git rm -r --cached` lines are quoted for the shell they are printed
+in, PowerShell or Git Bash, on Windows.
+Off Windows and in Git Bash, a path `shape-doctor.py` cannot print as itself is
+written `$'…'`: bash, zsh and ksh read that; dash (`/bin/sh` on Debian and
+Ubuntu) does not.
 
 </details>
 

docs/handbook.html

@@ -472,7 +472,7 @@
 
       <!-- reads README.md § preamble: blob ddadd23a162129f7e64fefce899105661440c05c -->
 
-      <!-- reads README.md § Starting a project in a new organisation: blob 3d4a01ffadc322f88dfffd9cef50b1c48c58b9b3 -->
+      <!-- reads README.md § Starting a project in a new organisation: blob e0d2b672082068b2df39ebf54801e068343a14c6 -->
 
       <!-- reads README.md § The three legs: blob 4ec313e8424665e41fc92a4147808e0bd4901d78 -->
 
@@ -612,7 +612,7 @@ <h4>The one thing to read before electing it</h4>
 
     <section id="start">
 
-      <!-- reads README.md § Starting a project in a new organisation: blob 3d4a01ffadc322f88dfffd9cef50b1c48c58b9b3 -->
+      <!-- reads README.md § Starting a project in a new organisation: blob e0d2b672082068b2df39ebf54801e068343a14c6 -->
 
       <p class="eyebrow">Setup</p>
       <h2>Start here</h2>
@@ -737,10 +737,13 @@ <h4>The tool offers the rest</h4>
           Printed commands are quoted for a POSIX shell, so paste them into Git Bash. Only
           <code>shape-doctor.py</code>&rsquo;s lines, <code>setup-project.py</code>&rsquo;s family
           lines and <code>family.py</code>&rsquo;s <code>NEXT</code>, <code>switch -c</code>,
-          <code>add</code> and <code>git rm -r --cached</code> lines are quoted for PowerShell, on
-          Windows. Off Windows, a path <code>shape-doctor.py</code> cannot print as itself is
-          written <code>$'&hellip;'</code>: bash, zsh and ksh read that; dash (<code>/bin/sh</code>
-          on Debian and Ubuntu) does not.</p>
+          <code>add</code>, <code>cd</code> and <code>git rm -r --cached</code> lines are quoted for
+          the shell they are printed in, PowerShell or Git Bash, on Windows. A shell started from
+          inside Git Bash inherits its <code>MSYSTEM</code>, which is how a tool tells Git Bash
+          apart, so a PowerShell started there is handed Git Bash&rsquo;s quoting, and a cmd.exe
+          started anywhere else is handed PowerShell&rsquo;s. Off Windows and in Git Bash, a path
+          <code>shape-doctor.py</code> cannot print as itself is written <code>$'&hellip;'</code>:
+          bash, zsh and ksh read that; dash (<code>/bin/sh</code> on Debian and Ubuntu) does not.</p>
         </div>
 
       </div>
@@ -1089,7 +1092,7 @@ <h4>What you have afterwards &mdash; the same on every platform</h4>
 
     <section id="partway">
 
-      <!-- reads README.md § Starting a project in a new organisation: blob 3d4a01ffadc322f88dfffd9cef50b1c48c58b9b3 -->
+      <!-- reads README.md § Starting a project in a new organisation: blob e0d2b672082068b2df39ebf54801e068343a14c6 -->
 
       <p class="eyebrow">Setup</p>
       <h2>If it fails part-way</h2>
@@ -1126,7 +1129,7 @@ <h2>If it fails part-way</h2>
 
     <section id="ci">
 
-      <!-- reads README.md § Starting a project in a new organisation: blob 3d4a01ffadc322f88dfffd9cef50b1c48c58b9b3 -->
+      <!-- reads README.md § Starting a project in a new organisation: blob e0d2b672082068b2df39ebf54801e068343a14c6 -->
 
       <!-- reads README.md § The three legs: blob 4ec313e8424665e41fc92a4147808e0bd4901d78 -->
 
@@ -1189,7 +1192,7 @@ <h2>Reading private legs in CI</h2>
 
     <section id="legs">
 
-      <!-- reads README.md § Starting a project in a new organisation: blob 3d4a01ffadc322f88dfffd9cef50b1c48c58b9b3 -->
+      <!-- reads README.md § Starting a project in a new organisation: blob e0d2b672082068b2df39ebf54801e068343a14c6 -->
 
       <!-- reads README.md § The three legs: blob 4ec313e8424665e41fc92a4147808e0bd4901d78 -->
 
@@ -1445,7 +1448,7 @@ <h3>The InkRouter example</h3>
 
     <section id="doublepin">
 
-      <!-- reads README.md § Starting a project in a new organisation: blob 3d4a01ffadc322f88dfffd9cef50b1c48c58b9b3 -->
+      <!-- reads README.md § Starting a project in a new organisation: blob e0d2b672082068b2df39ebf54801e068343a14c6 -->
 
       <!-- reads README.md § The double pin, and the lockstep invariant: blob 57fffa08ffad5476f8eae73dd3e8494a02e050c9 -->
 
@@ -1744,7 +1747,7 @@ <h2>Is this repository compliant? <code>openRepoShape --doctor</code></h2>
 
     <section id="park">
 
-      <!-- reads README.md § Starting a project in a new organisation: blob 3d4a01ffadc322f88dfffd9cef50b1c48c58b9b3 -->
+      <!-- reads README.md § Starting a project in a new organisation: blob e0d2b672082068b2df39ebf54801e068343a14c6 -->
 
       <!-- reads README.md § Carrying in-flight work to another workstation: blob b84512ad39c09085dfe6bf7ea694017f5e28c1dd -->
 

scripts/repo_shape.py

@@ -34,9 +34,11 @@
   - `spelled` and `escape_unencodable_stdout` — how both roots'
     `bootstrap.py` print a person's text: what a terminal must not be handed
     raw is escaped, and a stdout that cannot encode it never raises (#391).
-  - `shell_quoted` and `shell_line` — how `scripts/family.py` and a holder's
-    `scripts/siblings.py` spell a path in a command a person pastes, so that
-    it reaches the command as ONE argument in `sh` or PowerShell (#486).
+  - `shell_quoted` and `shell_line` — how `scripts/family.py` spells a path
+    in a command a person pastes, so that it reaches the command as ONE
+    argument in `sh` or PowerShell (#486), and
+    `host_shell_dialect`, which of the two a line printed here is for: Git
+    Bash on Windows gets `sh`'s (#711).
 
 This file is COPIED into a scaffolded assembly root by `scaffold-project.py`
 and its sha256 is recorded in that project's `contracts/shape-pin.yaml`, so an
@@ -3406,10 +3408,44 @@ def spelled(value: object) -> str:
 POWERSHELL_SINGLE_QUOTES = frozenset("'‘’‚‛")
 
 
+def host_shell_dialect(name: str | None = None, environ=None) -> str:
+    """Which shell a line printed on this host is quoted for, as the
+    `platform` `shell_quoted` takes: `"nt"` for PowerShell's dialect, and
+    `"posix"` for `sh`'s (#711). `name` and `environ` are `os.name` and
+    `os.environ` when None, so a test can ask about any host from any host.
+
+    THE RULE. A Windows host (`os.name` is `nt`) is PowerShell's, unless its
+    environment has a non-empty `MSYSTEM`: then the tool was run from Git
+    Bash, or another MSYS2 shell, which reads a line as `sh` does, so the
+    line gets `sh`'s quoting. Every other host is `sh`'s. It is asked each
+    time a line is quoted, not once at import, so the answer is the
+    environment's the line is printed in.
+
+    WHY `MSYSTEM`. Under Git Bash `os.name` is `nt`, as it is under
+    PowerShell, because the Python Git Bash runs is the same Windows Python,
+    so `os.name` cannot tell the two shells apart. Git Bash and every MSYS2
+    shell set `MSYSTEM` (`MINGW64`, `UCRT64`, `CLANGARM64`, `MSYS`, ...) and
+    hand it to every program they start; PowerShell and cmd.exe do not set
+    it. An EMPTY `MSYSTEM` names no MSYS2 shell, so it is not Git Bash.
+
+    WHAT IT DOES NOT COVER. A PowerShell or cmd.exe started from inside Git
+    Bash inherits `MSYSTEM`, so a tool run there is answered `sh`'s and
+    prints `sh`'s quoting into PowerShell: nothing the tool can read tells
+    that PowerShell from Git Bash, and this does not try. It answers the
+    quoting and the shell syntax around a word, and nothing about the
+    machine: `PYTHON` stays `python` under Git Bash, which runs the Windows
+    Python, and a path keeps its Windows spelling.
+    """
+    name = os.name if name is None else name
+    environ = os.environ if environ is None else environ
+    return "nt" if name == "nt" and not environ.get("MSYSTEM") else "posix"
+
+
 def shell_quoted(value: object, platform: str | None = None) -> str:
     """`value` as ONE word of a command a person pastes into the shell of
-    `platform` (`os.name` when None): bare where that shell reads every
-    character of it as itself, else whole, in single quotes (#486).
+    `platform` (`host_shell_dialect()` when None, #711): bare where that
+    shell reads every character of it as itself, else whole, in single
+    quotes (#486).
 
     THE DOCTOR'S RULE, `shape-doctor.py`'s `quote_arg`, which has quoted
     every path its NEXT lines print since #101/#102: `sh` and PowerShell are
@@ -3438,7 +3474,7 @@ def shell_quoted(value: object, platform: str | None = None) -> str:
     `quote_arg` still leaves it bare: a known gap, named where #486 lands.
     """
     text = str(value)
-    windows = (os.name if platform is None else platform) == "nt"
+    windows = (host_shell_dialect() if platform is None else platform) == "nt"
     bare = SHELL_BARE_NT if windows else SHELL_BARE_POSIX
     if not text.startswith("=") and bare.fullmatch(text):
         return text

setup-project.py

@@ -2687,32 +2687,55 @@ def clone_and_bootstrap(opts: Options, org: str, landing: Landing) -> dict:
 #: `SHELL_BARE_POSIX`. A backslash is not in it, so a Windows path is quoted.
 SHELL_BARE_POSIX = re.compile(r"[A-Za-z0-9_./:@%+=,-]+")
 
-#: A word this host's shell reads as itself, needing no quotes:
-#: `scripts/repo_shape.py`'s `SHELL_BARE_NT` on Windows, else its
-#: `SHELL_BARE_POSIX`. This file runs before any checkout of the standard
+#: A word PowerShell reads as itself: `scripts/repo_shape.py`'s
+#: `SHELL_BARE_NT`. This file runs before any checkout of the standard
 #: exists, so it carries its own copy of the rule, and
-#: `tests/test_family_printed_quoting.py` holds the two to one answer.
-SHELL_BARE = re.compile(r"[A-Za-z0-9_./:%+=\\-]+" if os.name == "nt"
-                        else SHELL_BARE_POSIX.pattern)
+#: `tests/test_git_bash_dialect.py` holds the two to one answer on every
+#: host, as `tests/test_family_printed_quoting.py` does on this one.
+SHELL_BARE_NT = re.compile(r"[A-Za-z0-9_./:%+=\\-]+")
+
+
+def host_shell_dialect(name=None, environ=None) -> str:
+    """`scripts/repo_shape.py`'s `host_shell_dialect`, as a copy, because
+    this file runs before any checkout of the standard exists (#711):
+    `"nt"`, PowerShell's dialect, on a Windows host whose environment has
+    no `MSYSTEM` or an empty one, and `"posix"`, `sh`'s, everywhere else,
+    Git Bash included. `name` and `environ` are `os.name` and `os.environ`
+    when None. Its docstring there says why `MSYSTEM`, and what it does not
+    cover: a PowerShell started from inside Git Bash inherits `MSYSTEM` and
+    is answered `sh`'s. `tests/test_git_bash_dialect.py` holds the two
+    copies to one answer."""
+    name = os.name if name is None else name
+    environ = os.environ if environ is None else environ
+    return "nt" if name == "nt" and not environ.get("MSYSTEM") else "posix"
 
 
 def shell_word(value, posix: bool = False) -> str:
-    """`value` as ONE word of a command pasted into this host's shell: bare
-    where every character is itself to it, else in single quotes, doubled
-    inside for PowerShell, closed-escaped-reopened for `sh` (#486). A
-    leading `=` is quoted too, which zsh would expand.
+    """`value` as ONE word of a command pasted into this host's shell, the
+    one `host_shell_dialect` answers (#711): bare where every character is
+    itself to it, else in single quotes, doubled inside for PowerShell,
+    closed-escaped-reopened for `sh` (#486). A leading `=` is quoted too,
+    which zsh would expand.
+
+    ASKED AT EACH CALL, NOT AT IMPORT. The alphabet a word may stay bare in
+    and the escape it is quoted with are one answer, taken from the
+    environment the line is printed in, where `MSYSTEM` says Git Bash. The
+    alphabet used to be fixed at import (`SHELL_BARE`, from `os.name`) and
+    the escape asked `os.name` at each call, two reads of one question.
 
     `posix` spells it for `sh` on EVERY host, Windows too: Git Bash reads
     the backslash of a bare `C:\\work` as an escape and an apostrophe doubled
     for PowerShell as two quotes, and #532 rules the printed commands
     POSIX-only. The lines #538 adds or changes pass it, as the scaffold's
     NEXT STEPS clone does (`shell_line(..., "posix")`); the family lines
-    (`family_next_command`) are #532's and still take this host's dialect."""
+    (`family_next_command`) are #532's and take the host's dialect, which
+    under Git Bash is `sh`'s (#711, L2-29)."""
     text = str(value)
-    bare = SHELL_BARE_POSIX if posix else SHELL_BARE
+    windows = not posix and host_shell_dialect() == "nt"
+    bare = SHELL_BARE_NT if windows else SHELL_BARE_POSIX
     if not text.startswith("=") and bare.fullmatch(text):
         return text
-    if os.name == "nt" and not posix:
+    if windows:
         return "'" + re.sub("(['\u2018\u2019\u201a\u201b])", r"\1\1",
                             text) + "'"
     return "'" + text.replace("'", "'\\''") + "'"