capture stderr from (process ...

[nigelbrown]

Hi,

I'm trying porting from python  to newlisp (of course) but python has possibility of assigning stderr output to a pipe when starting a process

eg from chatsniff1.0.py - http://chatsniff.sourceforge.net/">http://chatsniff.sourceforge.net/

 pipe = Popen('tethereal -i '+str(gDevices.index(gCurrentDevice) + 1)+' -l -V -R "aim || ymsg || msnms || jabber"', bufsize = 1, cwd = path, shell=True, stdin=PIPE, stdout=PIPE, stderr=PIPE, universal_newlines = True)



while (process in newlisp syntax is : (process str-command int-pipe-in int-pipe-out [int-win32-option])

i.e. only stdin stdout directable to pipes.

The code in nl-filesys.c is:



CELL * p_process(CELL * params)

{

char * command;

int forkResult;

int inpipe = 0, outpipe = 0;



params = getString(params, &command);

if(params != nilCell)

   {

   params = getInteger(params, (UINT*)&inpipe);

   getInteger(params, (UINT *)&outpipe);

   }



if((forkResult = fork()) == -1)

    return(nilCell);

if(forkResult == 0)

    {

    /* redirect stdin and stdout to pipe handles */

    if(inpipe)

        {

        close(STDIN_FILENO);

        if(dup2(inpipe, STDIN_FILENO) == -1) exit(0);

        close(inpipe);

        }

    if(outpipe)

        {

        close(STDOUT_FILENO);

        if(dup2(outpipe, STDOUT_FILENO) == -1) exit(0);

        close(outpipe);

        }



    system(command);

    exit(0);

    }

 could another option after [int-win32-option] be [int-pipe-err]

and newlisp do STDERR_FILENO to pipe?

Or is this not recommended?



Is there another way? - I see  in

return value thread ( http://www.alh.net/newlisp/phpbb/viewtopic.php?t=789">http://www.alh.net/newlisp/phpbb/viewtopic.php?t=789 ) that stderr can be handled from exec

Lutz:

> (exec "ls *.abc 2>&1")

("ls: *.abc: No such file or directory")

>

The 2>&1 spec tell ls to redirect error output to stdout.



but don't know enough about system() to know if that approach is possible for (process.



Any tips?



Nigel

[newdep]

Hello Nigel,



Did you try a combination of switching (device [int] )

to input/output/erro or pipe?

That could be a workaround, i did not test it though..



regards, Norman.

[nigelbrown]

Hi Norman,

I'm not sure what you mean by switching?



I've experimented with redirecting 2>&1 with a single line command and it works:

> (process "ls *.abc 2>&1" procin procout)

11118

> (read-line myin)

"ls: *.abc: No such file or directory"

>



Looking more at system() it does start a shell for the process so I'll use the 2>&1 approach.

Longer term newlisp might like to look at having optional capture of stderr to its own pipe (Lutz?).

full eg from python

         pipe = Popen('tethereal -i '+str(gDevices.index(gCurrentDevice) + 1)+' -l -V -R "aim || ymsg || msnms || jabber"', bufsize = 1, cwd = path, shell=True, stdin=PIPE, stdout=PIPE, stderr=PIPE, universal_newlines = True)

         global maintetherealpid

         maintetherealpid = pipe.pid

         pipe.stdin.close()

         f = pipe.stdout

         e = pipe.stderr

...



Nigel

[Lutz]

Currently only in Win32 stderr is redirected to the stdout pipe. On Linux/UNIX you can use the stderr redirection: 2>&1 on 'process' and 'exec'.



Yes, perhaps in the future an optional switch, although 2>&1 works already.



Lutz

[nigelbrown]

Hi Lutz,

I agree it's not a priority. However, it would allow easier recognition and handling of error or warning messages.



Regards

Nigel

[Lutz]

I have added an optiion for 8.7.5



Lutz

[nigelbrown]

Fantastic! Thank you Lutz, it will make my parsing of stdout much easier with stderr going elsewhere.



Regards

Nigel