HostFileEntry.ps1

function Add-HostFileEntry {
	[OutputType([String])]
	[CmdletBinding(
		SupportsShouldProcess=$true,
		ConfirmImpact="Medium")]
	param (
		[Parameter(Position=1, Mandatory=$true)]
		[ValidateNotNullOrEmpty()]
		[ValidatePattern("(?# Valid IP Address range 1.1.1.1 - 255.255.255.255)\A(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\z")]
		[string]$IPAddress,
		[Parameter(Position=2, Mandatory=$true)]
		[ValidateNotNullOrEmpty()]
		[string]$Hostname,
		[switch]$Force)
	Begin{
		$formats = @{
			"Begin" = "Begin {0}...";
			"Process" = "...processing {0}...";
			"End" = "...ending {0}";
		};
		Write-Verbose -Message ($formats.Begin -f $MyInvocation.MyCommand);
	} Process {
		Write-Verbose -Message ($formats.Process -f $MyInvocation.MyCommand);
		$hostFilePath = "$env:windir\System32\drivers\etc\hosts";    	
		$entry = "$IPAddress `t $Hostname";
		if(Test-HostFileEntry -IPAddress $IPAddress -Hostname $Hostname) {
			Write-Verbose -Message "$entry already exists";
			return $entry;
		}
		if($null -ne (Get-HostFileEntry -Hostname $Hostname) -and -not $Force) {
			throw "$Hostname already has an entry use -Force to overwrite";
		}
		if ($pscmdlet.ShouldProcess($entry)) {
			$entry | Out-File -Encoding ASCII -Append -FilePath $hostFilePath;
			return $entry;
		}
	} End {	
		Write-Verbose -Message ($formats.End -f $MyInvocation.MyCommand);
	}
}

function Remove-HostFileEntry {
	[OutputType([void])]
	[CmdletBinding(
		SupportsShouldProcess=$true,
		ConfirmImpact="Medium")]
	param (
		[Parameter(Position=1, Mandatory=$true)]
		[ValidateNotNullOrEmpty()]
		[string]$Hostname)
	Begin{
		$formats = @{
			"Begin" = "Begin {0}...";
			"Process" = "...processing {0}...";
			"End" = "...ending {0}";
		};
		Write-Verbose -Message ($formats.Begin -f $MyInvocation.MyCommand);
	} Process {
		Write-Verbose -Message ($formats.Process -f $MyInvocation.MyCommand);
		$hostFilePath = "$env:windir\System32\drivers\etc\hosts";    	
		$entry = " `t $Hostname";
		if($null -eq (Get-HostFileEntry -Hostname $Hostname)) {
			Write-Verbose -Message "$entry does not exists";
		}
		if ($pscmdlet.ShouldProcess($entry)) {
			Get-Content -Path $hostFilePath | Select-String $entry -NotMatch | Out-File -Encoding ASCII -FilePath $hostFilePath;
		}
	} End {	
		Write-Verbose -Message ($formats.End -f $MyInvocation.MyCommand);
	}
}

function Get-HostFileEntry {
	[OutputType([string])]
	[CmdletBinding(
		ConfirmImpact="None")]
	param (
		[Parameter(Position=1, Mandatory=$true)]
		[ValidateNotNullOrEmpty()]
		[string]$Hostname)
	Begin{
		$formats = @{
			"Begin" = "Begin {0}...";
			"Process" = "...processing {0}...";
			"End" = "...ending {0}";
		};
		Write-Verbose -Message ($formats.Begin -f $MyInvocation.MyCommand);
	} Process {
		Write-Verbose -Message ($formats.Process -f $MyInvocation.MyCommand);
		$hostFilePath = "$env:windir\System32\drivers\etc\hosts";    	
		Get-Content -Path $hostFilePath | Select-String $Hostname;
	} End {	
		Write-Verbose -Message ($formats.End -f $MyInvocation.MyCommand);
	}
}

function Test-HostFileEntry {
	[OutputType([bool])]
	[CmdletBinding(
		ConfirmImpact="None")]
	param (
		[Parameter(Position=1, Mandatory=$true)]
		[ValidateNotNullOrEmpty()]
		[ValidatePattern("(?# Valid IP Address range 1.1.1.1 - 255.255.255.255)\A(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\z")]
		[string]$IPAddress,
		[Parameter(Position=2, Mandatory=$true)]
		[ValidateNotNullOrEmpty()]
		[string]$Hostname)
	Begin{
		$formats = @{
			"Begin" = "Begin {0}...";
			"Process" = "...processing {0}...";
			"End" = "...ending {0}";
		};
		Write-Verbose -Message ($formats.Begin -f $MyInvocation.MyCommand);
	} Process {
		Write-Verbose -Message ($formats.Process -f $MyInvocation.MyCommand);
		$entry = "$IPAddress `t $Hostname";
		Get-HostFileEntry -Hostname $Hostname -eq $entry;
	} End {	
		Write-Verbose -Message ($formats.End -f $MyInvocation.MyCommand);
	}
}