How to write a Powershell file parameter that accepts a relative path - powershell

Question

The following sample code correctly reads both the PSD1 and the regular file when the path to the PSD1 is a fully qualified path (or when the current location is the same as the current directory).
It fails when supplied a relative path.
param (
[Parameter(Mandatory=$true)][System.IO.FileInfo]$PsdFile,
[Parameter(Mandatory=$false)][System.IO.FileInfo]$RegularFile = 'testfile'
)
$RegularFileContent = Get-Content $RegularFile
$PsdData = Import-LocalizedData -BaseDirectory $PsdFile.DirectoryName -FileName $PsdFile.Name
echo "regular file contents: $RegularFileContent"
echo "Psd data:"
echo $PsdData.Name
How can I fix this so the user can enter a relative path?
I believe the underlying problem is similar to the problem described in this post about FileInfo but I don't know how to incorporate Resolve-Path or similar into the parameter handling.

Answer 1

A lot of your question hinges on which relative you're referring to as that itself is relative. If you want the path to be relative to a user's working directory versus the script's root, you can accomplish that like so:
param(
[Parameter(Mandatory)]
[string]
$PsdFile,
[Parameter()] # Mandatory is $false by default
[string]
$RegularFile = 'testfile'
)
[System.IO.FileInfo]$psd = Join-Path -Path $PWD.Path -ChildPath $PsdFile
$data = Import-LocalizedData -BaseDirectory $psd.DirectoryName -FileName $PsdFile.Name
$content = Get-Content -Path $RegularFile
"regular file contents: $content"
"Psd data:" + $data.Name

Answer 2

param (
[Parameter(Mandatory = $true)]
[ValidateScript( {
if (-Not (Test-Path -Path $_ ) ) { throw "File not found." }
elseif (-Not (Test-Path -Path $_ -PathType Leaf) ) { throw "PsdFile should be a file." }
return $true
})]
[System.IO.FileInfo] $PsdFile,
[Parameter(Mandatory = $false)]
[ValidateScript( {
if (-Not (Test-Path -Path $_ ) ) { throw "File not found." }
elseif (-Not (Test-Path -Path $_ -PathType Leaf) ) { throw "PsdFile should be a file." }
return $true
})]
[System.IO.FileInfo] $RegularFile = 'testfile'
)
$PsdFile = (Resolve-Path -Path $PsdFile).Path;
$RegularFile = (Resolve-Path -Path $RegularFile).Path;
$RegularFileContent = Get-Content $RegularFile.FullName
$PsdData = Import-LocalizedData -BaseDirectory $PsdFile.DirectoryName -FileName $PsdFile.Name

Answer 3

I use a similar approach to #luri, incorporating ValidateScript to test if the path exists. This example tests specifically for files and throws an error if a directory is passed. This is useful for cases when the user is using <TAB> to quickly autocomplete paths for the -Path parameter.
function PathTestFunction
{
[CmdletBinding()]
param (
[Parameter(Mandatory,
ParameterSetName = 'Path',
ValueFromPipeline,
ValueFromPipelineByPropertyName
)]
[ValidateScript({
# Using Exists() because Test-Path doesn't test for system/hidden files
if ([System.IO.Directory]::Exists($(Resolve-Path -Path $_)))
{
throw "'$(Resolve-Path $_)' is a directory. Please use a file for the -Path parameter."
}
if ([System.IO.File]::Exists($(Resolve-Path -Path $_)) -eq $false)
{
$null = Resolve-Path $_ -ErrorVariable pathError
# Displays a full path name in the error message (vs a relative path if one was passed)
throw $pathError.Exception
}
return $true
})]
[System.IO.FileInfo]$Path
)
Get-Item $Path -Force
}
You could write a second ParameterSet to include a -LiteralPath param for added robustness - this would allow the user to pass a path that included wildcard chars (e.g. 'C:\Test[txt]File.txt').
Using <TAB> to autocomplete paths with wildcards would still work with the example above - but it wouldn't allow the user to type a full path name with unescaped wildcards in it, hence the need for both -Path and -LiteralPath parameters in that case:
'.\Test`[txt`]File.txt' would work with -Path (if using <TAB> to autocomplete path)
'C:\Test`[txt`]File.txt' would work with -Path (if using <TAB> to autocomplete path)
'C:\Test[txt]File.txt' would not work with -Path (if manually typed)