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.