A simple PowerShell implementation of the most basic functionality of Netcat

Send-NetworkData.ps1

function Send-NetworkData {
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [string]
        $Computer,

        [Parameter(Mandatory)]
        [ValidateRange(1, 65535)]
        [Int16]
        $Port,

        [Parameter(ValueFromPipeline)]
        [string[]]
        $Data,

        [System.Text.Encoding]
        $Encoding = [System.Text.Encoding]::ASCII,

        [TimeSpan]
        $Timeout = [System.Threading.Timeout]::InfiniteTimeSpan
    ) 

    begin {
        # establish the connection and a stream writer
        $Client = New-Object -TypeName System.Net.Sockets.TcpClient
        $Client.Connect($Computer, $Port)
        $Stream = $Client.GetStream()
        $Writer = New-Object -Type System.IO.StreamWriter -ArgumentList $Stream, $Encoding, $Client.SendBufferSize, $true
    }

    process {
        # send all the input data
        foreach ($Line in $Data) {
            $Writer.WriteLine($Line)
        }
    }

    end {
        # flush and close the connection send
        $Writer.Flush()
        $Writer.Dispose()
        $Client.Client.Shutdown('Send')

        # read the response
        $Stream.ReadTimeout = [System.Threading.Timeout]::Infinite
        if ($Timeout -ne [System.Threading.Timeout]::InfiniteTimeSpan) {
            $Stream.ReadTimeout = $Timeout.TotalMilliseconds
        }

        $Result = ''
        $Buffer = New-Object -TypeName System.Byte[] -ArgumentList $Client.ReceiveBufferSize
        do {
            try {
                $ByteCount = $Stream.Read($Buffer, 0, $Buffer.Length)
            } catch [System.IO.IOException] {
                $ByteCount = 0
            }
            if ($ByteCount -gt 0) {
                $Result += $Encoding.GetString($Buffer, 0, $ByteCount)
            }
        } while ($Stream.DataAvailable -or $Client.Client.Connected) 

        Write-Output $Result
        
        # cleanup
        $Stream.Dispose()
        $Client.Dispose()
    }

}

# pipe in a HTTP request:
'GET / HTTP/1.0', '' | Send-NetworkData -Computer www.powershellmagazine.com -Port 80

# Use the Data parameter to do the same:
Send-NetworkData -Data 'GET / HTTP/1.0', '' -Computer www.powershellmagazine.com -Port 80 

# As before but only wait 2 seconds for a response:
Send-NetworkData -Data 'GET / HTTP/1.0', '' -Computer www.powershellmagazine.com -Port 80 -Timeout 0:00:02

# Say hello to an SMTP server:
Send-NetworkData -Data "EHLO $Env:ComputerName", "QUIT" -Computer mail.example.com -Port 25

[Int16]::MaxValue is 32767 - [uint16] would probably be more appropriate for $Port

} while ($Stream.DataAvailable -or $Client.Client.Connected)

} while ($Stream.DataAvailable -and $Client.Client.Connected)

A complete Bash Netcat replacement,
echo -ne "ehlo [email protected]\r\nmail from:<[email protected]>\r\nrcpt to:<[email protected]>\r\ndata\r\nSubject: test\r\n\r\nHello, world\r\n.\r\nquit\r\n" | { mapfile -t lines; lines=("${lines[@]//$'\r'/}"); pslines=("${lines[@]/#/\"}"); pslines=("${pslines[@]/%/\"}"); pslines="${pslines[*]/%/,}"; pslines="${pslines:0: -1}"; powershell -noprofile -command '.\netcat.ps1' -Computer SERVER -Port 25 -Data "${pslines}" -Timeout "0:00:02"; }

Using =$True in [Parameter(...=$True)] makes a similar script compatible with PowerShell 2.