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

hosts.ps1

#
# Powershell Functions for adding/removing/showing entries to the hosts file.
#
# Known limitations:
# - does not handle entries with comments afterwards ("<ip>    <host>    # comment")
#
Function Use-RunAs {
    # Check if script is running as Administrator and if not use RunAs
    # Use Check Switch to check if admin
    param([Switch]$Check)
    
    # Detecting OS Platform, win32nt for Windows or unix for Linux/Unix
    $OSPlatform = (([System.Environment]::OSVersion.Platform).ToString()).ToLower()
    if ($OSPlatform -eq "unix") {
        Write-Warning "Detected Linux/Unix OS, you don't need this, use sudo"
        exit # Quit this session of powershell
    } 
    
    $IsAdmin = ([Security.Principal.WindowsPrincipal] [Security.Principal.WindowsIdentity]::GetCurrent()`
    ).IsInRole([Security.Principal.WindowsBuiltInRole] "Administrator")
    if ($Check) { return $IsAdmin }
    if ($MyInvocation.ScriptName -ne "") {
        if (-not $IsAdmin) {
            try {
                # Detecting Powershell (powershell.exe) or Powershell Core (pwsh), will return true if Powershell Core (pwsh)
                if ($IsCoreCLR) { $PowerShellCmdLine = "pwsh.exe" } else { $PowerShellCmdLine = "powershell.exe" }
                $arg = "-file `"$($MyInvocation.ScriptName)`""
                Start-Process "$PSHOME\$PowerShellCmdLine" -Verb Runas -ArgumentList $arg -ErrorAction 'stop'
            }
            catch {
                Write-Warning "Error - Failed to restart script with runas"
                break
            }
            exit # Quit this session of powershell 
        }
    }
    else {
        Write-Warning "Error - Script must be saved as a .ps1 file first"
        break
    }
}

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]
        }
    }
}

#
# Example Usage
#
Use-RunAs 
"Script Running As Administrator"
Start-Sleep 3

$file = "$env:SystemRoot" + "\System32\drivers\etc\hosts"

try {
    if ($args[0] -eq "add") {
    
        if ($args.count -lt 3) {
            throw "Not enough arguments for add."
        }
        else {
            Add-Host -HostsFile $file -IP $args[1] -Hostname $args[2]
        }
        
    }
    elseif ($args[0] -eq "remove") {
    
        if ($args.count -lt 2) {
            throw "Not enough arguments for remove."
        }
        else {
            Remove-Host -HostsFile $file -Hostname $args[1]
        }
        
    }
    elseif ($args[0] -eq "show") {
        Show-Hosts -HostsFile $file
    }
    else {
        throw "Invalid operation '" + $args[0] + "' - 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"
}