Powershell script for adding/removing/viewing entries to the hosts file.

hosts.ps1

#
# Powershell script for adding/removing/showing entries to the hosts file.
#
# Known limitations:
# - does not handle entries with comments afterwards ("<ip>    <host>    # comment")
#
# Original Script: https://gist.github.com/markembling/173887/1824b370be3fe468faceaed5f39b12bad010a417
# Modified Script: https://gist.github.com/andreymir/405b924d32dace51af2b
# Modified Script: https://gist.github.com/lantrix/052dff5737957aae4e25
#

<#
    .SYNOPSIS
        Powershell script for modifying entries in the hosts file.
    .PARAMETER Action
        The action you would like to perform (add, remove, show)
    .PARAMETER HostsFile
        The hosts file to modify
    .PARAMETER IP
        The IP address for the hosts entry
    .PARAMETER Hostname
        The hostname for the entry
    .EXAMPLE
        .\hosts.ps1 -Action add -HostsFile "C:\Windows\System32\drivers\etc\hosts" -IP "127.0.0.1" -Hostname "myserverhost"
    .EXAMPLE
        .\hosts.ps1 add "dkittell.local" "127.0.0.1" "C:\Windows\System32\drivers\etc\hosts"
    .EXAMPLE
        .\hosts.ps1 add "dkittell.local" "127.0.0.1"
    .EXAMPLE
        .\hosts.ps1 -Action remove -HostsFile "C:\Windows\System32\drivers\etc\hosts" -Hostname "myserverhost"
    .EXAMPLE
        .\hosts.ps1 remove "dkittell.local"
    .EXAMPLE
        .\hosts.ps1 -Action show -HostsFile "C:\Windows\System32\drivers\etc\hosts"
    .EXAMPLE
        .\hosts.ps1 show 'C:\WINDOWS\System32\drivers\etc\hosts'
    .EXAMPLE
        .\hosts.ps1 show
#>

param
(
  [Parameter(Mandatory = $true,Position = 0)]
  [ValidateSet("add","remove","show")]
  [string]$Action,

  [Parameter(Position = 1)]
  [string]$Hostname,

  [Parameter(Position = 2)]
  [System.Net.IPAddress]$IP,

  [Parameter(Position = 3)]
  [string]$HostsFile = "$env:SystemRoot" + "\System32\drivers\etc\hosts"

)

#region Functions
function add-host {
<#
.SYNOPSIS
    Powershell function for adding entries to the hosts file.
.PARAMETER HostsFile
    The hosts file to modify
.PARAMETER IP
    The IP address for the hosts entry
.PARAMETER Hostname
    The hostname for the entry
.EXAMPLE
    Add-Host -HostsFile "C:\Windows\System32\drivers\etc\hosts" -IP "127.0.0.1" -Hostname "myserverhost"
#>
  [CmdletBinding()]
  param(
    [Parameter(Mandatory = $true)] [string]$HostsFile,
    [Parameter(Mandatory = $true)] [string]$IP,
    [Parameter(Mandatory = $true)] [string]$Hostname
  )
  remove-host -HostsFile $HostsFile -hostname $Hostname
  $IP + "`t`t" + $Hostname | Out-File -Encoding ASCII -Append $HostsFile
}

function remove-host {
<#
        .SYNOPSIS
        Powershell function for removing entries from a hosts file.
        .DESCRIPTION
        Known limitations: does not handle entries with comments afterwards ("<ip> <host> # comment")
        .PARAMETER HostsFile
        The hosts file to modify
        .PARAMETER Hostname
        The hostname for the entry
        .EXAMPLE
        Remove-Host -HostsFile "C:\Windows\System32\drivers\etc\hosts" -Hostname "myserverhost"
    #>
  [CmdletBinding()]
  param(
    [Parameter(Mandatory = $true)] [string]$HostsFile,
    [Parameter(Mandatory = $true)] [string]$Hostname
  )
  $c = Get-Content $HostsFile
  $newLines = @()

  foreach ($line in $c) {
    $bits = [regex]::Split($line,'\t+')
    if ($bits.count -eq 2) {
      if ($bits[1] -ne $Hostname) {
        $newLines += $line
      }
    } else {
      $newLines += $line
    }
  }

  # Write file
  Clear-Content $HostsFile
  foreach ($line in $newLines) {
    $line | Out-File -Encoding ASCII -Append $HostsFile
  }
}

function Show-Hosts {
<#
        .SYNOPSIS
        Powershell function for showing entries in a hosts file.
        .DESCRIPTION
        Known limitations: does not handle entries with comments afterwards ("<ip> <host> # comment")
        .PARAMETER HostsFile
        The hosts file to access
        .EXAMPLE
        Show-Hosts -HostsFile "C:\Windows\System32\drivers\etc\hosts"
    #>
  [CmdletBinding()]
  param(
    [Parameter(Mandatory = $true)] [string]$HostsFile
  )
  $c = Get-Content $HostsFile
  foreach ($line in $c) {
    $bits = [regex]::Split($line,'\t+')
    if ($bits.count -eq 2) {
      Write-Host $bits[0] `t`t $bits[1]
    }
  }
}

#endregion Functions

#region Take Action
try {
  if ($Action -eq "add") {

    if ($IP -eq '' -or $Hostname -eq '') {
      throw "Not enough arguments for add."
    } else {
      add-host -HostsFile $HostsFile -ip $IP -hostname $Hostname
      #Show-Hosts -HostsFile $HostsFile
    }

  } elseif ($Action -eq "remove") {

    if ($Hostname -eq '') {
      throw "Not enough arguments for remove."
    } else {
      remove-host $HostsFile $Hostname
      #Show-Hosts -HostsFile $HostsFile
    }

  } elseif ($Action -eq "show") {
    Show-Hosts -HostsFile $HostsFile
  } else {
    throw "Invalid operation '" + $Action + "' - must be one of 'add', 'remove', 'show'."
  }
} catch {
  Write-Host $error[0]
  Write-Host "`nUsage: hosts add <ip> <hostname>`n       hosts remove <hostname>`n       hosts show"
}
#endregion Take Action