[fpc-devel] Running programs with output redirection

[Ludo Brands]

> There seems to exist an issue with (output) redirection, when 
> I try to 
> run an external program from code. What I want to achieve is this:
> 
> In a Win32 console I can run
>  >diff -r dir1 dir2 > diff.txt
> 
> When I use e.g. Exec('diff', args), diff complains about an excess 
> argument, it works when "> diff.txt" is removed. With other 
> functions I 
> had less luck (ExecuteProcess, CreateProcess...), no output at all.
> 
> Now I assume that output redirection is a shell feature, not 
> available 
> in direct invocation of an external program. Right?
> 

Redirection is indeed a shell function.

> Does there exist a simple way to run "diff", and to redirect 
> its output 
> into an file? A batch file? Platform independence would be 
> nice, of course.
> 

Start the shell instead of diff:

  exec('cmd','/c diff -r dir1 dir2 > diff.txt');

The /c tells the shell to execute the command and exit immediately. 

Ludo