I'm cross developing a program in free pascal running FreeVision. When running under Linux / Busybox; I'm attempting to mount a device to scan it for a set of files. Since I'm running a TUI (Text User Interface); I cannot have the BusyBox mount command printing failure information to the screen where it corrupts the TUI. The pascal code:

Exec( '/bin/mount', '/dev/'+ aline +' /media/' + aline + ' &> /dev/null');

When running:

Exec( '/bin/mount', '/dev/'+ aline +' /media/' + aline );

I see "device busy" STDERR messages appear on the screen. However, when I try to redirect using the ' &> /dev/null' it appears as tho the BusyBox executable is being passed ' &> /dev/null' as a parameter and isn't taking it as the appropriate redirection command.

I tried the following kludge instead:

var
OurPipe    : Text;
         popen( OurPipe, '/bin/mount /dev/'+ aline +' /media/' + aline, 'R');
         Try
             if (fpgeterrno=0) then Flush (OurPipe)
             ELSE MessageBox ('mount pipe error ' + IntToStr(fpgeterrno), nil,
                  mfError or mfOKButton);
         Finally
             PClose( OurPipe );
         END;

however, I'm getting an Accessviolation. unsure if I'm even going down the right path.

Any other suggestions?

2010/2/17 Zitt Zitterkopf :

Exec( '/bin/mount', '/dev/'+ aline +' /media/' + aline + ' &> /dev/null');

Try:

Exec( '/bin/mount', '/dev/'+ aline +' /media/' + aline + ' 1>/dev/null');

for redirecting STDOUT or

Exec( '/bin/mount', '/dev/'+ aline +' /media/' + aline + ' 2>/dev/null
1>/dev/null');

for redirecting STDOUT and STDERR.

This works for me:

var f: textfile;
    s: string;
begin
  if popen(f, '/bin/mount /dev/'+ aline +' /media/' + aline + ' 2>&1',
'r') = 0 then
  begin
    readln(f,s);
    // test output 's'
    pclose(f);
  end
  else
    error := fpgeterrno;   // failed
end;

This puts stdout and stderr into one pipe however. There must be some way to read from stdout and stderr separately, maybe using TProcess, but I've never needed it so I don't know how.

In our previous episode, cobines said:

Try
fpsystem

it executes a shell, and &> 1> 2> are shell commands, and won't work with direct execution commands like exec (which is old anyway, use executeprocess)

This puts stdout and stderr into one pipe however. There must be some way to read from stdout and stderr separately, maybe using TProcess, but I've never needed it so I don't know how.

TProcess is definitely the thing to look at.

I wanted to thank you guys for you help with this and other problems I posted recently.

My project entered beta today... and I'm expecting it to be opensourced in the coming mth or so.

I ended up using the suggestion of using the fpsystem() call which seemed to work well except that it does not work if you do not have a bash shell installed in your environment. I worked around this by sym linking sh to bash to make it work under busybox; however, someone may want to look to see if the fpsystem call can be shell independant.

John

From:
To:
Subject: Exec(), Linux, and /dev/null redirection
Date: Tue, 16 Feb 2010 16:34:08 -0800

I'm cross developing a program in free pascal running FreeVision. When running under Linux / Busybox; I'm attempting to mount a device to scan it for a set of files. Since I'm running a TUI (Text User Interface); I cannot have the BusyBox mount command printing failure information to the screen where it corrupts the TUI. The pascal code:

Exec( '/bin/mount', '/dev/'+ aline +' /media/' + aline + ' &> /dev/null');

When running:

Exec( '/bin/mount', '/dev/'+ aline +' /media/' + aline );

I see "device busy" STDERR messages appear on the screen. However, when I try to redirect using the ' &> /dev/null' it appears as tho the BusyBox executable is being passed ' &> /dev/null' as a parameter and isn't taking it as the appropriate redirection command.

I tried the following kludge instead:
var
OurPipe    : Text;
         popen( OurPipe, '/bin/mount /dev/'+ aline +' /media/' + aline, 'R');
         Try
             if (fpgeterrno=0) then Flush (OurPipe)
             ELSE MessageBox ('mount pipe error ' + IntToStr(fpgeterrno), nil,
                  mfError or mfOKButton);
         Finally
             PClose( OurPipe );
         END;

however, I'm getting an Accessviolation. unsure if I'm even going down the right path.

Any other suggestions?