# Powershell Safe Invocation

> Use when writing or running PowerShell on Windows, especially native programs, quoted paths, escaping, pwsh, Start-Process, file operations, or shell troubleshooting.

- Skill: `openbmb/powershell-safe-invocation` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add openbmb/powershell-safe-invocation`
- Raw SKILL.md: https://api.skillmd.com/api/skills/openbmb/powershell-safe-invocation/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: OpenBMB (https://skillmd.com/u/openbmb)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/openbmb/powershell-safe-invocation

---


# PowerShell Safe Invocation

## Shell

Use PowerShell 7 through `pwsh.exe` unless Windows PowerShell 5.1 is explicitly required.

When the active shell is uncertain, verify:

```powershell
$PSVersionTable.PSVersion
$PSNativeCommandArgumentPassing
```

Do not assume installing PowerShell 7 makes `powershell.exe` use PowerShell 7:

- `pwsh.exe` = PowerShell 7
- `powershell.exe` = Windows PowerShell 5.1

## Native Programs

Never construct one large command string when arguments can be passed separately.

Use:

```powershell
$exe = 'C:\Path With Spaces\tool.exe'
$args = @(
    '--input'
    'C:\Data Folder\input.json'
    '--flag'
)

& $exe @args

$exitCode = $LASTEXITCODE
if ($exitCode -ne 0) {
    throw "$exe failed with exit code $exitCode"
}
```

Rules:

- Treat every native argument as one array item.
- Invoke executable paths stored in variables with `&`.
- Capture `$LASTEXITCODE` immediately.
- Do not use `Invoke-Expression`.
- Do not add a `cmd.exe /c` layer merely to launch an executable.
- Do not use Bash-style `\"` escaping in PowerShell.

## Cmdlets

Use hashtable splatting for PowerShell cmdlets:

```powershell
$params = @{
    LiteralPath = 'C:\Data[1]\input.txt'
    Destination = 'C:\Output'
    Force       = $true
    ErrorAction = 'Stop'
}

Copy-Item @params
```

Use `-LiteralPath` for real paths unless wildcard expansion is intentional.

Do not use `$LASTEXITCODE` to test a PowerShell cmdlet. Use terminating errors:

```powershell
$ErrorActionPreference = 'Stop'
```

## Complex Commands

Avoid deeply quoted commands such as:

```text
cmd.exe /c pwsh.exe -Command "..."
```

For multiline code, nested quotes, JSON, XML, regular expressions, pipelines, redirection, or non-ASCII paths:

1. Write a temporary `.ps1` file.
2. Execute it with:

```text
pwsh.exe -NoLogo -NoProfile -NonInteractive -File script.ps1
```

Prefer `-File` over `-Command` for anything beyond a short, simple expression.

Do not add `-ExecutionPolicy Bypass` unless execution policy is actually blocking a trusted script.

## Strings And Multiline Code

- Use single quotes for literal strings and paths.
- Use double quotes only when PowerShell expansion is needed.
- Avoid backtick line continuation; use arrays, hashtables, splatting, parentheses, or script blocks.
- For JSON, create objects and use `ConvertTo-Json`; do not hand-escape JSON.
- Use single-quoted here-strings for literal multiline text.
- Specify text encoding explicitly when another tool consumes the file.

## Start-Process

For normal foreground execution, use:

```powershell
& $exe @args
```

Use `Start-Process` only for elevation, new/hidden windows, detached launch, or shell behavior.

`Start-Process -ArgumentList` joins values into a command-line string and is not a reliable structured-argument API.

When a separate process is required and arguments are complex, use:

```powershell
$psi = [System.Diagnostics.ProcessStartInfo]::new()
$psi.FileName = $exe
$psi.UseShellExecute = $false

foreach ($arg in $args) {
    $psi.ArgumentList.Add($arg)
}

$process = [System.Diagnostics.Process]::Start($psi)
$process.WaitForExit()

if ($process.ExitCode -ne 0) {
    throw "Process failed with exit code $($process.ExitCode)"
}
```

## File Operations

Before recursive delete, move, or overwrite:

- Resolve the absolute root and target paths.
- Verify the target is inside the intended root.
- Reject empty, root-level, or unexpected paths.
- Keep filesystem mutations in PowerShell instead of passing paths to another shell.

## Decision Order

Choose the simplest safe option:

1. PowerShell cmdlet.
2. `& $exe @args`.
3. Temporary `.ps1` file with `pwsh.exe -File`.
4. `ProcessStartInfo.ArgumentList`.
5. `Start-Process` when its special behavior is required.
6. `cmd.exe /c` only when cmd semantics are required.
7. `Invoke-Expression` only as a tightly controlled last resort.

For uncommon cases, prefer the same decision order and simplify the invocation until each parser boundary is explicit.