[fpc-pascal] POpen en PClose

[Adriaan van Os]

On 20/07/2026 12:02, Marco van de Voort via fpc-pascal wrote:
>
> Op 20-7-2026 om 11:57 schreef Michael Van Canneyt via fpc-pascal:
>>>>
>>>> I am looking at the implementation of POpen and PClose in the 
>>>> runtime-library for Darwin (or more general for UNIX). It seems 
>>>> like it doesn't call into libc popen and pclose, but instead 
>>>> follows its own implementation in unix.pp in POpen_internal. I am 
>>>> just curious to know the reason.
>>>>
>>> Phew, that was over twenty years ago, but afaik the reason is that 
>>> libc popen and pclose us C FILE descriptors, which the RTL in 
>>> general doesn't use to avoid a mix of functions with pascal and C 
>>> file types.
>>>
>>> So popen/pclose are a more high level (FILE * using) part of libc, 
>>> while we tend to only use the basis.
>>
>> Glad our memories agree on this :-) 
>
> Well aside from the fact that FreeBSD was the architecture where the 
> baseunix/unix RTL  was done. The port to Linux was only done later :-)
>
> This shows the tension a bit between libc the system lib, and libc the 
> C runtime. We are only interested in the system lib part.

Another question. POpen has a file as input parameter. The description 
in unix.pp says

   "Starts the program in 'Prog' and makes it's input or out put the
   other end of a pipe. If rw is 'w' or 'W', then whatever is written to
   F, will be read from stdin by the program in 'Prog'. The inverse is true
   for 'r' or 'R' : whatever the program in 'Prog' writes to stdout, can be
   read from 'f'."

So, for write mode, it doesn't use StdOut but a file. Does this imply 
that (for writing) I can call POpen with multiple files, forking and 
running multiple programs, writing to each of these child processes 
through a different pipe ?

Regards,

Adriaan van Os