ln Command in PowerShell

Set-StrictMode -Off;

# bodge the ln command
$usage = "usage: ln [-s] <target> [link_name]"

$src = '
using System;
using System.Runtime.InteropServices;
public class kernel {
    [DllImport("kernel32.dll")]
    [return: System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.I1)]
    public static extern bool CreateSymbolicLink(string lpSymlinkFileName, string lpTargetFileName, uint dwFlags);

    [DllImport("kernel32.dll", SetLastError=true, CharSet=CharSet.Auto)]
    public static extern bool CreateHardLink(string lpFileName, string lpExistingFileName, IntPtr lpSecurityAttributes);
}'

function isadmin {
    $id = [System.Security.Principal.WindowsIdentity]::GetCurrent()
    $p = new-object System.Security.Principal.WindowsPrincipal $id
    $p.isinrole([security.principal.windowsbuiltinrole]::administrator)
}

function symlink($target, $link_name, $is_dir) {
    # CreateSymbolicLink:
    #     http://msdn.microsoft.com/en-us/library/aa363866.aspx
    $dwFlags = 0
    if($is_dir) { $dwFlags = 1 }

    $kernel = add-type $src -passthru
    $result = $kernel::createsymboliclink($link_name, $target, $dwFlags)

    if(!$result) { "failed!"; exit 1 } # mysterious
}

function hardlink($target, $link_name) {
    # CreateHardLink:
    #     http://msdn.microsoft.com/en-us/library/aa363860.aspx
    $kernel = add-type $src -passthru
    $result = $kernel::createhardlink($link_name, $target, [intptr]::zero)

    if(!$result) { "failed!"; exit 1 } # mysterious
}

$symbolic = $false
$target = $args[0]
$link_name = $args[1]
$is_dir = $false

if($target -like '-s') {
    $symbolic = $true
    $target = $args[1]
    $link_name = $args[2]
}

if(!$target) { "ln: target is required"; $usage; exit 1 }
if(!$link_name) {
    # create link in working dir, with same name as target
    $link_name = "$pwd\$(split-path $target -leaf)"
} elseif(!([io.path]::ispathrooted($link_name))) {
    $link_name = "$pwd\$link_name"
}

if(!(test-path $target)) {
    "ln: $target`: No such file or directory"; exit 1
}

if(test-path $link_name) {
    "ln: $link_name`: File exists"
}

$abstarget = "$(resolve-path $target)"
if([io.directory]::exists($abstarget)) {
    $is_dir = $true
}

if($abstarget -eq $link_name) {
    "ln: target and link_name are the same"; $usage; exit 1
}

if(!$symbolic -and $is_dir) {
    "ln: Can't create hard links for directories: use -s for symbolic link"; $usage; exit 1
}

if(!(isadmin)) {
    if(gcm 'sudo' -ea silent) {
        "ln: Must run elevated: try using 'sudo ln ...'."
    } else {
        if(gcm 'scoop' -ea silent) {
            "ln: Must run elevated: you can install 'sudo' by running 'scoop install sudo'."
        } else { "ln: Must run elevated" }
    }
    exit 1
}

if($symbolic) {
    symlink $target $link_name $is_dir
} else {
    hardlink $target $link_name
}

exit 0