Hello,
Environment variables are local to each *process*, they inherit the
them from their parent when a process is created. If a process modifies
its environment variables it is only visible in that process and
possibly in any child process it creates.
A common way to get values from a sub process is using pipes. They are
available through the functions TSystem::OpenPipe() and
TSystem::ClosePipe(). You can either write to the standard input
of the sub process or read from the standard output.
OpenPipe() returns a "C" library FILE pointer that can be used
with fgets() to read the data (or fprintf() if you need to provide
input)
Regards,
Marten.
On Fri, 2003-08-01 at 09:26, Valeri Fine wrote:
> Hello,
> You may try
>
> http://root.cern.ch/root/htmldoc/TSystem.html#TSystem:Setenv
>
> method to set that.
>
> However this is still shell specific.
> I think it is not a good idea to provide the communication between two
> processes via the shell env variable. It looks simple but it is error
> prone.
>
> I agree with Olivier's statement
> "I guess you should find another way to send the run number outside
> ROOT"
>
> Best regards, Valeri
>
> > -----Original Message-----
> > From: owner-roottalk@pcroot.cern.ch
> [mailto:owner-roottalk@pcroot.cern.ch]
> > On Behalf Of Olivier Couet
> > Sent: Friday, August 01, 2003 5:25 AM
> > To: Meiwen
> > Cc: rt
> > Subject: Re: [ROOT] help
> >
> >
> > Hello,
> >
> > I think your problem comes from the fact that gSystem->Exec starts a
> new
> > shell. So your variable is defined during the short time this new
> shell
> > is alive but then doesn't exist in the shell in which ROOT started. In
> > order to demonstrate this effect I have created the following very
> simple
> > example:
> >
> > --- file runnb.C
> > {
> > gSystem->Exec("export AAA=hello");
> > printf("%s\n", gSystem->Getenv("ROOTSYS"));
> > printf("%s\n", gSystem->Getenv("AAA"));
> > }
> > ---
> >
> > The output of this macro is:
> >
> > root [0] .x runnb.C
> > /home/couet/rootpro
> >
> > root [1]
> >
> > as you see the variable ROOTSYS is known because it was set in the
> shell
> > in which ROOT started, but AAA is blank because the shell in which it
> was
> > set finished. I guess you should find an other way to send the run
> number
> > outside ROOT. May be write it into a file ?
> >
> > Cheers, Olivier
> >
> >
> > On Fri, 1 Aug 2003, Meiwen wrote:
> >
> > > Dear rooters
> > > I need to get the value of parameter Run_Number and have
> written a
> > small test program as following:
> > >
> > > {
> > > gROOT->Reset();
> > > char *RUNNR = new char[100];
> > >
> > > sprintf(RUNNR, "export Run_Number=`getvalue runctl@krunc runnr |
> grep
> > value | awk '{print $3}'`");
> > >
> > > gSystem->Exec(RUNNR);
> > >
> > > cout << "Run_Number = " << gSystem->Getenv("Run_Number") << endl;
> > >
> > >
> > > }
> > >
> > > The problem is the result of Run_Number is empty. But when I
> executed
> > the command
> > >
> > > export Run_Number=`getvalue runctl@krunc runnr | grep value | awk
> > '{print $3}'`
> > > echo $Run_Number
> > >
> > > I got the real value Run_Number. Could you help me?
> > >
> > > thanks a lot Wen
> Mei
> > >
> >
> > --
> > Org: CERN - European Laboratory for Particle Physics.
> > Mail: 1211 Geneve 23 - Switzerland Mailbox:
> J25910
> > E-Mail: Olivier.Couet@cern.ch Phone: +41
> 22
> > 7676522
> > WWW: http://cern.ch/Olivier.Couet/ Fax: +41
> 22
> > 7677155
--
Maarten Ballintijn <maartenb@mit.edu>
Massachusetts Institute of Technology
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