Dup2

   

Declaration:

Procedure Dup2 (Var OldFile, NewFile : Text) ;

Description:

Makes NewFile an exact copy of OldFile, after having flushed the buffer of OldFile. NewFile can be an assigned file. If newfile was open, it is closed first. Due to the buffering mechanism of Pascal, this has not the same functionality as the dup2 (2) call in C. The internal Pascal buffers are not the same after this call, but when the buffers are flushed (e.g. after output), the output is sent to the same file. Doing an lseek will, however, work as in C, i.e. doing a lseek will change the fileposition in both files.

Errors:

Linuxerror is used to report errors.

sys_ebadf

OldFile hasn't been assigned.

sys_emfile

Maximum number of open files for the process is reached.

See also:

Dup, Dup2 (2)

Example

program Example31;

{ Program to demonstrate the Dup function. }

uses linux;

var f : text;
    i : longint;
    
begin
  Assign (f,'text.txt');
  Rewrite (F);
  For i:=1 to 10 do writeln (F,'Line : ',i);
  if not dup2 (output,f) then 
    Writeln ('Dup2 Failed !');
  writeln ('This is written to stdout.');
  writeln (f,'This is written to the dup file, and flushed');
  flush(f);
  writeln;
  { Remove file. Comment this if you want to check flushing.}
  Unlink ('text.txt');
end.