How do I check if my Delphi console app is redirected to a file or pipe?

Question

I have a console app that must disable or enable some operations when output is redirected (externally) to a file or pipe (myapp.exe > Foo.bar)

How I can check if my Delphi console app is redirected to a file or pipe?

Answer 1

you can use the GetStdHandle and GetFileType functions.

first you retrieve the console output handle using the GetStdHandle function and then you can check the type of the handle with the GetFileType function.

{$APPTYPE CONSOLE}

{$R *.res}

uses
  Windows,
  SysUtils;


function ConsoleRedirected: Boolean;
var
  FileType : DWORD;
begin
  FileType:= GetFileType(GetStdHandle(STD_OUTPUT_HANDLE));
  Result  := (FileType=FILE_TYPE_PIPE) or (FileType=FILE_TYPE_DISK);
end;


begin
  try
    if ConsoleRedirected then
      Writeln('Hello From File')
    else
      Writeln('Hello Console');
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

Answer 2

The approach I present here feels hacky but I can't find a better way to detect whether or not the standard output has been redirected away from a screen console. The approach using GetFileType cannot detect all forms of redirection since some redirections are to devices of type FILE_TYPE_CHAR.

---

Call GetConsoleMode() passing the standard output handle. If GetConsoleMode() fails then your console has been redirected.

program RedirectionDetection;
{$APPTYPE CONSOLE}
uses
  Windows;

function ConsoleRedirected: Boolean;
var
  Mode: DWORD;
begin
  Result := not GetConsoleMode(GetStdHandle(STD_OUTPUT_HANDLE), Mode);
end;

begin
  if ConsoleRedirected then begin
    Writeln('I have been redirected');
  end else begin
    Writeln('I am a console');
    Readln;
  end;
end.