PS> 'hello' | Out-File ./test.txt -Encoding ascii
PS> Invoke-WebRequest -Method Post -InFile ./test.txt http://httpbin.org/post

> Invoke-WebRequest -InFile .\test.txt -Method Post http://httpbin.org/post

StatusCode        : 200
StatusDescription : OK
Content           : {
                      "args": {},
                      "data": "",
                      "files": {},
                      "form": {
                        "hello\r\n": ""
                      },
                      "headers": {
                        "Content-Length": "7",
                        "Content-Type": "application/x-www-form-urlencoded",
                        "Host": "...
RawContent        : HTTP/1.1 200 OK
                    Connection: keep-alive
                    Access-Control-Allow-Origin: *
                    Access-Control-Allow-Credentials: true
                    Content-Length: 405
                    Content-Type: application/json
                    Date: Mon, 21 Nov 2016 22:36:29 GM...
Forms             : {}
Headers           : {[Connection, keep-alive], [Access-Control-Allow-Origin, *], [Access-Control-Allow-Credentials, true], [Content-Length, 405]...}
Images            : {}
InputFields       : {}
Links             : {}
ParsedHtml        : mshtml.HTMLDocumentClass
RawContentLength  : 405

C:\src\scratch
> Invoke-WebRequest -InFile .\test.txt -Method Post http://httpbin.org/post
Invoke-WebRequest : Error while copying content to a stream.
At line:1 char:1
+ Invoke-WebRequest -InFile .\test.txt -Method Post http://httpbin.org/ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (Method: POST, R...m-urlencoded
}:HttpRequestMessage) [Invoke-WebRequest], HttpRequestException
    + FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeWebRequestCommand

C:\src\scratch
> $error[0].Exception.ToString()
System.Net.Http.HttpRequestException: Error while copying content to a stream. ---> System.ObjectDisposedException: Cannot access a closed file.
   at System.IO.Win32FileStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
   at System.IO.FileStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
   at System.Net.Http.StreamToStreamCopy.<CopyAsyncAnyStreamToAnyStreamCore>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Net.Http.HttpContent.<CopyToAsyncCore>d__44.MoveNext()
   --- End of inner exception stack trace ---
   at System.Net.Http.HttpContent.<CopyToAsyncCore>d__44.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Net.Http.WinHttpHandler.<InternalSendRequestBodyAsync>d__126.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Net.Http.WinHttpHandler.<StartRequest>d__101.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Net.Http.HttpClient.<FinishSendAsync>d__58.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.PowerShell.Commands.WebRequestPSCmdlet.GetResponse(HttpClient client, HttpRequestMessage request)
   at Microsoft.PowerShell.Commands.WebRequestPSCmdlet.ProcessRecord()

~/git/scratch
> Invoke-WebRequest -InFile ./test.txt http://httpbin.org/post                                                                                                                                                                                     
Invoke-WebRequest : Cannot access a closed file.
At line:1 char:1
+ Invoke-WebRequest -InFile ./test.txt https://www.google.com
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Invoke-WebRequest], ObjectDisposedException
    + FullyQualifiedErrorId : System.ObjectDisposedException,Microsoft.PowerShell.Commands.InvokeWebRequestCommand
 
~/git/scratch
> $error[0].Exception.ToString()                                                                                                                                                                                                                              
System.ObjectDisposedException: Cannot access a closed file.
   at System.IO.UnixFileStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
   at System.IO.FileStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
   at System.Net.Http.DelegatingStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
   at System.Net.Http.CurlHandler.MultiAgent.<>c__DisplayClass42_0.<TransferDataFromRequestStream>b__0(Task`1 readStream, Object s)
   at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Net.Http.CurlHandler.MultiAgent.TransferDataFromRequestStream(IntPtr buffer, Int32 length, EasyRequest easy)
   at System.Net.Http.CurlHandler.MultiAgent.CurlSendCallback(IntPtr buffer, UInt64 size, UInt64 nitems, IntPtr context)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Net.Http.HttpClient.<FinishSendAsync>d__58.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.PowerShell.Commands.WebRequestPSCmdlet.GetResponse(HttpClient client, HttpRequestMessage request)
   at Microsoft.PowerShell.Commands.WebRequestPSCmdlet.ProcessRecord()
   at System.Management.Automation.Cmdlet.DoProcessRecord()
   at System.Management.Automation.CommandProcessor.ProcessRecord()