How about some PowerShell instead?

# Echo command-line input

    $args -join " "

(Yes, it's a single line.)

# Count duplicates in a file

    $lines = @{}
    foreach ($path in $args) {
        cat $path | % { $lines[$_] += 1 }
    }
    $lines.GetEnumerator() | % { if ($_.Value -gt 1) { "$($_.Value)`t$($_.Name)" } }

# GET request

    param($url)
    irm $url

# Parallel GET requests

    $before = get-date
    $args | % -parallel {
        $res = iwr $_
        $after = get-date
        $time = ($after - $using:before).TotalSeconds
        "${time}s`t$($res.RawContentLength)`t$_"
    } -ThrottleLimit 12345
    $after = get-date
    $time = ($after - $before).TotalSeconds
    "${time}s elapsed"

I'm showcasing a few different ways of doing things: using $args, using the param directive; using foreach, or % which is an alias of ForEach-Object; irm for Invoke-RestMethod, iwr for Invoke-WebRequest...