Sanitizing an input to create a valid output file name

Question

I have a function that creates an ACL permission table X levels deep given a root folder and how many levels you'd like to go. I want to name the output file based on the root folder given, but obviously file names can't have certain characters in them.
How do I replace all "< > : " / \ | ? *" characters with
underscores? 
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Answer 1

If anyone cares, here's my final code:
Function Get-FoldersToDepth {
Param(
[String]$Path = $PWD,
[String]$Filter = "*",
[Byte]$ToDepth = 255,
[Byte]$CurrentDepth = 0,
[Switch]$DebugMode
$CurrentDepth++
If ($DebugMode) { $DebugPreference = "Continue" }
Get-ChildItem -Directory $Path | %{
$_ | ?{ $_.Name -Like $Filter }
If ($_.PsIsContainer) {
If ($CurrentDepth -le $ToDepth) {
# Callback to this function
Get-FoldersToDepth -Path $_.FullName -Filter $Filter `
-ToDepth $ToDepth -CurrentDepth $CurrentDepth
} Else {
Write-Debug $("Skipping GCI for Folder: $($_.FullName) " + `
"(Why: Current depth $CurrentDepth vs limit depth $ToDepth)")
$date = get-date -UFormat "%d.%m.%Y"
$a = "<style>"
$a = $a + "BODY{background-color: #F0F0F0;}"
$a = $a + "TABLE{border-width: 1px;border-style: solid;border-color: #D0D0D0;border-collapse: collapse;padding: 2px}"
$a = $a + "TH{border-width: 1px;padding: 2px;border-style: solid;border-color: #D0D0D0;background-color: #BFFFFF}"
$a = $a + "TD{border-width: 1px;padding: 2px;border-style: solid;border-color: #D0D0D0;background-color: #BFBFBF}"
$a = $a + "</style>"
Function CreatePermissionMap {
Param(
[string]$Path = $PWD,
[string]$filter = "*",
[Byte]$ToDepth = 255
$folderprep = get-folderstodepth -path $path -ToDepth $ToDepth -filter $filter
$folders = $folderprep.fullname
$output = $path -replace '[<>:"/\\|?*]','_'
ForEach ($folder in $folders)
get-accesscontrolentry -InputObject $folder | select path, principal, AceType, AccessMaskDisplay, AppliesTo | ConvertTo-Html -Head $a -body "<H2>ACL entries for: $folder</H2>" | out-file -Append h:\powershell\temp\$output.$date.html
I'm likely to spend the next 2 hours figuring out how to make all those tables line up
[email protected]