Remove-Hostnames.ps1
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function Remove-Hostnames { <# .SYNOPSIS Removes one or more hostnames from the hosts file. .DESCRIPTION The hosts file is used to map hostnames to IP addresses. .PARAMETER Hostnames One or more hostnames to remove from the hosts file. .PARAMETER RetryCount How many times to try writing to the hosts file before giving up? Defaults to 30. IMPORTANT: It's advised to retry as many times as possible to avoid transient locks on the hosts file causing a failure. .EXAMPLE Remove-TecBoxHostnames foobar Description ----------- Assume the following line was previously added to the hosts file: 127.0.0.1 foobar After running "Remove-TecBoxHostnames foobar" the hosts file no longer contains this line. .EXAMPLE Remove-TecBoxHostnames foo Description ----------- Assume the following line was previously added to the hosts file: 127.0.0.1 foobar foo bar After running "Remove-TecBoxHostnames foo" the line in the hosts file is updated to remove the specified hostname ("foo"): 127.0.0.1 foobar bar .EXAMPLE Remove-TecBoxTecBoxHostnames foo, bar Description ----------- Assume the following line was previously added to the hosts file: 127.0.0.1 foobar foo bar After running "Remove-TecBoxHostnames foo, bar" the line in the hosts file is updated to remove the specified hostnames ("foo" and "bar"): 127.0.0.1 foobar .NOTES This script must be run with administrator privileges. CRITICAL: The consequence of a failure is the hosts file will be left empty. TODO: Improvement robustness to prevent a failure resulting in an empty hosts file #> [CmdletBinding()] param( [parameter(Mandatory = $true, ValueFromPipeline = $true)] [string[]] $Hostnames, [int] $RetryCount = 30 ) begin { Set-StrictMode -Version Latest $ErrorActionPreference = "Stop" function Execute-WithRetry([ScriptBlock] $command) { $attemptCount = 0 $operationIncomplete = $true $maxFailures = $RetryCount $sleepBetweenFailures = 2 while ($operationIncomplete -and $attemptCount -lt $maxFailures) { $attemptCount = ($attemptCount + 1) if ($attemptCount -ge 2) { Write-Verbose "Waiting for $sleepBetweenFailures seconds before retrying..." Start-Sleep -s $sleepBetweenFailures Write-Verbose "Retrying..." } try { # Call the script block & $command $operationIncomplete = $false } catch [System.Exception] { if ($attemptCount -lt ($maxFailures)) { Write-Warning ("Attempt $attemptCount of $maxFailures failed: " + $_.Exception.Message) } else { throw } } } } function CreateHostsEntryObject( [string] $ipAddress, [string[]] $hostnames, <# [string] #> $comment) #HACK: never $null if type is specified { $hostsEntry = New-Object PSObject $hostsEntry | Add-Member NoteProperty -Name "IpAddress" ` -Value $ipAddress [System.Collections.ArrayList] $hostnamesList = New-Object System.Collections.ArrayList $hostsEntry | Add-Member NoteProperty -Name "Hostnames" ` -Value $hostnamesList If ($hostnames -ne $null) { $hostnames | foreach { $hostsEntry.Hostnames.Add($_) | Out-Null } } $hostsEntry | Add-Member NoteProperty -Name "Comment" -Value $comment return $hostsEntry } function ParseHostsEntry( [string] $line) { $hostsEntry = CreateHostsEntryObject Write-Debug "Parsing hosts entry: $line" If ($line.Contains("#") -eq $true) { If ($line -eq "#") { $hostsEntry.Comment = [string]::Empty } Else { $hostsEntry.Comment = $line.Substring($line.IndexOf("#") + 1) } $line = $line.Substring(0, $line.IndexOf("#")) } $line = $line.Trim() If ($line.Length -gt 0) { $hostsEntry.IpAddress = ($line -Split "\s+")[0] Write-Debug "Parsed address: $($hostsEntry.IpAddress)" [string[]] $parsedHostnames = $line.Substring( $hostsEntry.IpAddress.Length + 1).Trim() -Split "\s+" Write-Debug ("Parsed hostnames ($($parsedHostnames.Length)):" ` + " $parsedHostnames") $parsedHostnames | foreach { $hostsEntry.Hostnames.Add($_) | Out-Null } } return $hostsEntry } function ParseHostsFile { $hostsEntries = New-Object System.Collections.ArrayList [string] $hostsFile = $env:WINDIR + "\System32\drivers\etc\hosts" If ((Test-Path $hostsFile) -eq $false) { Write-Verbose "Hosts file does not exist." } Else { [string[]] $hostsContent = Get-Content $hostsFile $hostsContent | foreach { $hostsEntry = ParseHostsEntry $_ $hostsEntries.Add($hostsEntry) | Out-Null } } # HACK: Return an array (containing the ArrayList) to avoid issue with # PowerShell returning $null (when hosts file does not exist) return ,$hostsEntries } function UpdateHostsFile( $hostsEntries = $(Throw "Value cannot be null: hostsEntries")) { Write-Verbose "Updatings hosts file..." [string] $hostsFile = $env:WINDIR + "\System32\drivers\etc\hosts" $buffer = New-Object System.Text.StringBuilder $hostsEntries | foreach { If ([string]::IsNullOrEmpty($_.IpAddress) -eq $false) { $buffer.Append($_.IpAddress) | Out-Null $buffer.Append("`t") | Out-Null } If ($_.Hostnames -ne $null) { [bool] $firstHostname = $true $_.Hostnames | foreach { If ($firstHostname -eq $false) { $buffer.Append(" ") | Out-Null } Else { $firstHostname = $false } $buffer.Append($_) | Out-Null } } If ($_.Comment -ne $null) { If ([string]::IsNullOrEmpty($_.IpAddress) -eq $false) { $buffer.Append(" ") | Out-Null } $buffer.Append("#") | Out-Null $buffer.Append($_.Comment) | Out-Null } $buffer.Append([System.Environment]::NewLine) | Out-Null } [string] $hostsContent = $buffer.ToString() $hostsContent = $hostsContent.Trim() Execute-WithRetry { Set-Content -Path $hostsFile -Value $hostsContent -Force -Encoding ASCII } Write-Verbose "Successfully updated hosts file." } [bool] $isInputFromPipeline = ($PSBoundParameters.ContainsKey("Hostnames") -eq $false) [int] $pendingUpdates = 0 [Collections.ArrayList] $hostsEntries = ParseHostsFile } process { If ($isInputFromPipeline -eq $true) { $items = $_ } Else { $items = $Hostnames } $items | foreach { [string] $hostname = $_ for ([int] $i = 0; $i -lt $hostsEntries.Count; $i++) { $hostsEntry = $hostsEntries[$i] Write-Debug "Hosts entry: $hostsEntry" If ($hostsEntry.Hostnames.Count -eq 0) { continue } for ([int] $j = 0; $j -lt $hostsEntry.Hostnames.Count; $j++) { [string] $parsedHostname = $hostsEntry.Hostnames[$j] Write-Debug ("Comparing specified hostname" ` + " ($hostname) to existing hostname" ` + " ($parsedHostname)...") If ([string]::Compare($hostname, $parsedHostname, $true) -eq 0) { Write-Debug "Removing hostname ($hostname) from host entry ($hostsEntry)..." $hostsEntry.Hostnames.RemoveAt($j) $j-- $pendingUpdates++ } } If ($hostsEntry.Hostnames.Count -eq 0) { Write-Debug ("Removing host entry (because it no longer specifies" ` + " any hostnames)...") $hostsEntries.RemoveAt($i) $i-- } } } } end { If ($pendingUpdates -eq 0) { Write-Verbose "No changes to the hosts file are necessary." return } Write-Verbose ("There are $pendingUpdates pending update(s) to the hosts" ` + " file.") UpdateHostsFile $hostsEntries } } |