Command-line password generator

mkpw.ps1

<#
.SYNOPSIS
    CLI password generator using RNGCryptoServiceProvider
.DESCRIPTION
    Generates a password at the command-line using a cryptographically-secure random
    number generator.
.PARAMETER Length
    How long of a password to generate.
.PARAMETER Chars
    Chars from which to generate the password. The default set avoids ambiguous characters
    (e.g. uppercase i and lowercase L).
.Parameter CopyToClipboard
    Copy the password to the clipboard.
.EXAMPLE
    mkpw
    Generate a password
.EXAMPLE
    mkpw 20
    Generate a 20-character password
.EXAMPLE
    mkpw -Length 64 -Chars abcdef0123456789
    Generate a 64 character (32-byte) hexadecimal string
#>

param(
    [ValidateRange(1, 1000)]
    [Int]
    $Length = 16,

    [ValidateLength(1, 255)]
    [String]
    $Chars = "ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz123456789",

    [switch]
    $CopyToClipboard = $false
)

$result = ""
$rnd = New-Object System.Security.Cryptography.RNGCryptoServiceProvider
$byte = New-Object System.Byte[] 1

while ($result.Length -lt $Length) {
    # Note: avoids modulo bias
    do {
        $rnd.GetBytes($byte)
    } while ($byte[0] -ge (255 - 255 % $Chars.Length))

    $result += $Chars[$byte[0] % $Chars.Length]
}

if ($CopyToClipboard) {
    $result | Set-Clipboard
}

$result