I've got a little program that just pings. It runs. I get a 0 error return, but there doesn't seem to be any output:

-rw-r--r-- 1 root wheel 0 21 May 11:09 output.txt

So it's re-writing the output.txt file, but the
written(AstringList.Text) isn't putting anything there.

This is almost a direct copy from the examples, so I'm not clear what I'm doing wrong. It could be that TStringList isn't working as I thought - because even the 'stdout:' doesn't appear in the file 'output.txt'. Or it could be that AProcess.Output isn't working.

Any suggestions?
Free Pascal Compiler version 2.6.4 [2014/02/26] for i386 OS/X 10.9.3

Program nmp(input,output);
uses
  Classes, SysUtils,  Process;
var
  AProcess: TProcess;
  AStringList: TStringList;
  n :Integer;
begin { main }
  for n := 0 to 20 do
        begin { for }
        AStringList := TStringList.Create;
        AProcess := TProcess.Create(nil);
        AProcess.Executable := 'ping';
        AProcess.Parameters.Add('-c 1');
        AProcess.Parameters.Add('www.freepascal.org');
        AProcess.Options := AProcess.Options + [poWaitOnExit, poUsePipes];
        AProcess.Execute;
        AStringList.SaveToFile('output.txt');
        Writeln(n,' Execution Over: Exit Status: ',AProcess.ExitStatus);
        AStringList.Add('stdout:');
        AStringList.LoadFromStream(Aprocess.Output);
        AStringList.Add('stderr:');
        AStringList.LoadFromStream(AProcess.Stderr);
        AStringList.LoadFromStream(AProcess.Output);
        writeln(AStringList.Text);
        AstringList.Free;
        AProcess.Free;
        end; {for}
close(output) {added just in case it was losing the write}
end.

Move it here:
AStringList.SaveToFile('output.txt');

Mattias

Sorry, I misled you. I did move it higher up, earlier, to test something, and I forgot to put it back.

This version has exactly the same behaviour:

-rw-r--r-- 1 peterbrooks wheel 0 21 May 13:00 output.txt

Program nmp(input,output);
uses
  Classes, SysUtils,  Process;
var
  AProcess: TProcess;
  AStringList: TStringList;
  n :Integer;
begin { main }
  for n := 0 to 20 do
begin { for }
  AStringList := TStringList.Create;
  AProcess := TProcess.Create(nil);
  AProcess.Executable := 'ping';
  AProcess.Parameters.Add('-c 1');
  AProcess.Parameters.Add('www.freepascal.org');
  AProcess.Options := AProcess.Options + [poWaitOnExit, poUsePipes];
  AProcess.Execute;
  Writeln(n,' Execution Over: Exit Status: ',AProcess.ExitStatus);
  AStringList.Add('stdout:');
  AStringList.LoadFromStream(Aprocess.Output);
  AStringList.Add('stderr:');
  AStringList.LoadFromStream(AProcess.Stderr);
  AStringList.LoadFromStream(AProcess.Output);
  AStringList.SaveToFile('output.txt');
  writeln(AStringList.Text);
AstringList.Free;
AProcess.Free;
end; {for}
close(output);
close(input);
end.

What is this replacing the current content with?

TProcess needs the full path: '/bin/ping'

TProcess needs to be extended to raise an exception in this case.

Mattias

Peter,

I've been working with running Linux on an Android tablet (without rooting the device) and one thing I've seen mentioned is that ping requires higher priorities (I don't remember the details). You can read more here:
http://turbocontrol.com/gnuroot.htm

Best regards,
Paul
www.TurboControl.com

Does that page of yours apply to OSX then?

Unfortunately, I've tried both the full path and just the name - apparently TProcess is supposed to look in the path - and it does work. When it is called, it returns a '0' indicating successful completion.

I just tried it again with /sbin/ping instead of ping and the behaviour is just the same.

Is there an easier way to print the stream that comes back from TProcess? I think that the problem is in TStringList.

Peter Brooks wrote

Unfortunately, I've tried both the full path and just the name - apparently TProcess is supposed to look in the path - and it does work. When it is called, it returns a '0' indicating successful completion.

/disclaimer: haven't looked at your code/
voicechecker & fpcup contains a wrapper around TProcess[1] that lets you easily get output. See the convenience functions ExecuteCommand etc.

An example of use: pinging a host on OSX, can be found in voicechecker's pingtest.pas [2]

It works well for voicechecker, fpcup and some other projects

[1]
https://bitbucket.org/reiniero/voicechecker/src/01d4337c5ed948aeafe57d892d33db98c0a9f742/processutils.pas?at=default

[2]
https://bitbucket.org/reiniero/voicechecker/src/01d4337c5ed948aeafe57d892d33db98c0a9f742/pingtest.pas?at=default

I've already said that you're repeatedly overwriting the content.

Perhaps you need to further analyze the output when you get result code 0 as the ping command may have succeeded but the hosts were unreachable. Voicechecker's voicecheckermain.pas uses this when calling pingtest:

function TForm1.AnalyzeUnixPing(OutputText: TStringList): boolean;
begin
  result:=false;
  if (pos(' 0.0% packet loss',OutputText.Text)>0) then //OSX
    result:=true
  else if (pos(' 0% packet loss',OutputText.Text)>0) then //Linux
    result:=true;
end;

and

  ATest:=TRemoteCommandTest.Create;
  ATest.TestName:='RouterInternetUp';
... details ...
  TRemoteCommandTest(ATest).Command:='ping -c 1 www.google.com; echo "";
echo ""';
  TRemoteCommandTest(ATest);
... more code...

Peter Brooks wrote

AStringList.LoadFromStream(Aprocess.Output); AStringList.LoadFromStream(AProcess.Stderr); AStringList.LoadFromStream(AProcess.Output);

[quote]
LoadFromStream loads the contents of Stream into the stringlist. Each line in the stream (as marked by the end-of-line marker of the particular OS the application runs on) becomes one string in the stringlist. This action replaces the contents of the stringlist, it does not append the strings to the current content.
[/quote]

those LoadFromStream calls are overwriting the contents of your stringlist... note the last sentence in the above quote from
http://www.freepascal.org/docs-html/rtl/classes/tstrings.loadfromstream.html

you need to figure out how to run through your streams and AStringList.Add() the entries to your stringlist

*OR*

you need to have another set of stringlists for those process outputs and then use AStringList.AddStrings()

*OR*

you need to AStringList.Assign() another string list, print/save it, AStringList.Assign() the next string list, print/save it and so on... as LoadFromStream, Assign replaces the current contents of AStringList with the new contents...

FWIW: if you are using the "improved example" on
http://wiki.freepascal.org/Executing_External_Programs then you should note that it does state that it is flawed and that you should use the code in the next example "reading large output" which waits till the end and then loads the stream into the stringlist and then you can manipulate it from there...

Yes, thank you. The best thing I've learned is to be suspicious of examples...

I've got it now, thank you all for the assistance.

I took AStringList.Add() to mean that it added the string to the list of strings - I was wrong..

I did note that the example said that it was flawed, but, foolishly, as it turned out, I thought it meant 'flawed' rather than 'doesn't work at all'.

Do you mean this example:
http://wiki.freepascal.org/Executing_External_Programs#An_improved_example_.28but_not_correct_yet.29

It works here.
What is wrong?

Mattias

Peter Brooks wrote

I took AStringList.Add() to mean that it added the string to the list of strings - I was wrong..

How were you wrong about that? That's exactly what it does.

Looks to me you were wrong about LoadFromStream.

In our previous episode, Mattias Gaertner said:

Not using

http://wiki.freepascal.org/Executing_External_Programs#.28Process..29RunCommand

:-)