Restrict a function parameter to known choices.
PowerShell: ValidateSet rejects unsupported values before the function body executes.
$ErrorActionPreference = 'Stop'
Set-StrictMode -Version Latest
function Get-Mode { param([ValidateSet('fast','safe')][string]$Mode) $Mode }
Get-Mode -Mode safe
try { Get-Mode -Mode invalid } catch { 'Rejected' }Expected output EXAMPLE
safe Rejected
Details
Requires PowerShell 7. Save as snippet.ps1 and run pwsh -NoProfile -File snippet.ps1. Tested on Linux; these examples use portable paths and cmdlets. ValidateSet rejects unsupported values before the function body executes.
Tested on Ubuntu 24.04.5 LTS · · PowerShell 7.6.6 · powershell 7.6.6-1.deb
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Snippet process uid 65534 with a read-only root filesystem and temporary working files. Networking disabled. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged process) / C.UTF-8
- Interpreter invocation
pwsh -NoLogo -NoProfile -NonInteractive -File snippet.ps1- Container image ID
sha256:ec91410a8f6ec3e985830b5e3a0560306d36f8c1c5ccd91a6699abe707123fa3- Code SHA-256
22d995e0d3ecd94f8abb287d361380b459d30d08c7dd284ae254c6ee40b22835- Dependencies
- powershell 7.6.6-1.deb
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
# No input files required.
Observed standard output
safe Rejected
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.