Windows Shell

---
name: windows-shell
description: Write shell commands that actually run on Windows. Use whenever the working machine is Windows and a command, script, path, or setup step is involved, and whenever a command has already failed with "not recognized", "cannot find path", "No such file or directory", a python3 or NUL problem, or CRLF warnings. Covers PowerShell, cmd, Git Bash, WSL, and the traps that differ between them.
---

# Windows shell

The failure is not that Windows is hard. It is that the model has read a million
Linux commands and reaches for them, then burns three turns discovering the
machine is not Linux.

This is the second largest problem area in the Claude Code issue tracker. The
fixes below are specific and each one is a real, repeated failure.

## First: know which shell you are in

Windows gives you at least four, and they are not compatible.

| Shell | `ls` | Paths | Notes |
| --- | --- | --- | --- |
| PowerShell | alias for `Get-ChildItem` | `C:\x` or `C:/x` | the default in most tools |
| cmd.exe | `dir` only | `C:\x` | almost never what you want |
| Git Bash (MSYS2) | real `ls` | `/c/Users/...` | POSIX tools, but not Linux |
| WSL | real `ls` | `/mnt/c/...` | a different filesystem, different installed software |

**Check before guessing:**

```powershell
$PSVersionTable.PSVersion
```

```bash
uname -s
```

If `uname` prints `MINGW64_NT` you are in Git Bash. If it prints `Linux` inside
Windows you are in WSL, and software installed on Windows is not on your PATH.

Read `references/traps.md` before writing anything non-trivial.

## The rules that prevent most failures

**1. Never write `rm -rf` on a Windows path.** In PowerShell it is not a
command. In Git Bash it works and will happily delete outside the project. Use
`Remove-Item -Recurse -Force` in PowerShell, and in Git Bash prefer deleting
specific paths.

**2. `/dev/null` does not exist in PowerShell.** Use `$null`:

```powershell
Get-ChildItem 2>$null
```

In Git Bash `/dev/null` works normally. `NUL` is the cmd.exe form, and writing
it in the wrong shell creates a file literally named `NUL` that is then awkward
to delete.

**3. Quote every path.** Windows paths contain spaces far more often than Unix
ones: `C:\Program Files\...`, `C:\Users\First Last\...`. An unquoted path is the
single most common failure.

**4. Backslashes are escapes in bash.** In Git Bash, write `C:/Users/x` with
forward slashes, or `/c/Users/x`. Windows APIs accept forward slashes almost
everywhere.

**5. `python3` may be a Microsoft Store stub.** On many machines
`python3` resolves to an App Execution Alias that prints `Python` and exits 0
without running anything. A script can appear to pass while never executing.
Verify before trusting a result:

```bash
python3 -c "import sys; print(sys.version)"
```

If that does not print a version, find the real interpreter under
`%LOCALAPPDATA%\Programs\Python\`.

**6. Newly installed tools are not on PATH in the current session.** After
`winget install`, the current shell still has the old PATH. Either start a new
shell or call the binary by full path. Do not conclude the install failed.

**7. Unicode output can crash a script.** The default console encoding is a
regional code page, not UTF-8, so printing an emoji or non-Latin text raises
`UnicodeEncodeError`. Force it:

```bash
PYTHONIOENCODING=utf-8 python script.py
```

**8. Line endings.** Git will warn `LF will be replaced by CRLF`. That is
normal and not an error. Do not "fix" it by rewriting files. If a shell script
must stay LF, set it in `.gitattributes`.

**9. Path length.** The classic limit is 260 characters and deep
`node_modules` trees still hit it. If a build fails with a path error, that is
usually why.

**10. Case insensitivity hides bugs.** `import './Button'` resolving a file
named `button.tsx` works on Windows and fails on the Linux CI box. Match the
case exactly.

## Translating a Unix command

| Unix | PowerShell |
| --- | --- |
| `rm -rf dir` | `Remove-Item dir -Recurse -Force` |
| `cp -r a b` | `Copy-Item a b -Recurse` |
| `mv a b` | `Move-Item a b` |
| `cat f` | `Get-Content f` |
| `grep p f` | `Select-String p f` |
| `which x` | `Get-Command x` |
| `export A=1` | `$env:A = '1'` |
| `A=1 cmd` | `$env:A='1'; cmd` |
| `touch f` | `New-Item f -ItemType File` |
| `ls -la` | `Get-ChildItem -Force` |
| `cmd &` | `Start-Process cmd` |
| `head -5 f` | `Get-Content f -TotalCount 5` |
| `tail -5 f` | `Get-Content f -Tail 5` |
| `&&` | `;` for sequence, `-and` for logic |
| `2>/dev/null` | `2>$null` |

PowerShell has no `&&` in older versions. In PowerShell 7 it exists, in 5.1 it
does not, and 5.1 still ships with Windows.

## When a command fails

Read the error before retrying. These map one to one:

- `'x' is not recognized` → wrong shell, or the tool is not on PATH in this session
- `cannot find path` → unquoted path, or backslash eaten by bash
- `No such file or directory` on a `C:\` path → you are in Git Bash, use `/c/...`
- `Access is denied` on delete → the file is open, or you need `-Force`
- exit 0 with no output from a Python script → the Store stub, see rule 5

Do not retry the same command hoping for a different result. Change the shell or
change the syntax.

---

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> Fixed with windows-shell, a free skill from Fine Structure (https://finestructure.ai).