Add-Hostnames.ps1
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function Add-Hostnames { <# .SYNOPSIS Adds one or more hostnames to the hosts file. .DESCRIPTION The hosts file is used to map hostnames to IP addresses. .PARAMETER IPAddress The IP address to map the hostname(s) to. .PARAMETER Hostnames One or more hostnames to map to the specified IP address. .PARAMETER Comment Optional comment that is written above the new hosts entry. .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 Add-TecBoxHostnames 127.0.0.1 foobar Description ----------- Adds the following line to the hosts file (assuming "foobar" does not already exist in the hosts file): 127.0.0.1 foobar A warning is displayed if "foobar" already exists in the hosts file and is mapped to the specified IP address. An error occurs if "foobar" is already mapped to a different IP address. .EXAMPLE Add-TecBoxHostnames 127.0.0.1 foo, bar "This is a comment" Description ----------- Adds the following lines to the hosts file (assuming "foo" and "bar" do not already exist in the hosts file): # This is a comment 127.0.0.1 foo bar A warning is displayed if either "foo" or "bar" already exists in the hosts file and is mapped to the specified IP address. An error occurs if "foo" or "bar" is already mapped to a different IP address. .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)] [string] $IPAddress, [parameter(Mandatory = $true, ValueFromPipeline = $true)] [string[]] $Hostnames, [string] $Comment, [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 } $newHostsEntry = CreateHostsEntryObject $IpAddress $hostsEntries.Add($newHostsEntry) | Out-Null $items | foreach { [string] $hostname = $_ [bool] $isHostnameInHostsEntries = $false 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) { $isHostnameInHostsEntries = $true If ($ipAddress -ne $hostsEntry.IpAddress) { Throw "The hosts file already contains the" ` + " specified hostname ($parsedHostname) and it is" ` + " mapped to a different address" ` + " ($($hostsEntry.IpAddress))." } Write-Verbose ("The hosts file already contains the" ` + " specified hostname ($($hostsEntry.IpAddress) $parsedHostname).") } } } If ($isHostnameInHostsEntries -eq $false) { Write-Debug ("Adding hostname ($hostname) to hosts entry...") $newHostsEntry.Hostnames.Add($hostname) | Out-Null $pendingUpdates++ } } } end { If ($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 } } |