Re: gSystem->Exec() : memory of variables

From: Georg Troska <georg.troska_at_uni-dortmund.de>
Date: Wed, 9 Mar 2011 13:46:25 +0100

Hi,

a variable is not an alias.
doing in bash

# A="xclock"
# echo $A

will not work either.
Probably not the best way, but

root[] # gSystem->SetEnv("A","xclock")
root[] # gSystem->Exec("`echo $A`")

will work.

Georg

> 
> but the folllowing doesn't "work":
> 
> root [1] gSystem->Setenv("amiGetDatasetEVNTInfo","'python /afs/cern.ch/atlas/software/releases/16.6.2/AtlasCore/16.6.2/Database/Bookkeeping/AMIClients/pyAMI/python/amiGetDatasetEVNTInfo.py'")
> root [2] gSystem->Exec("amiGetDatasetEVNTInfo")
> sh: amiGetDatasetEVNTInfo: command not found
> 
> while in unix :
> alias amiGetDatasetEVNTInfo='python /afs/cern.ch/atlas/software/releases/16.6.2/AtlasCore/16.6.2/Database/Bookkeeping/AMIClients/pyAMI/python/amiGetDatasetEVNTInfo.py
> amiGetDatasetENVInfo
> "works"
> 
> would you have a hint ?
> 
> ===============
> 
> Dario Berzano a écrit :

>> Hello,
>>
>> each gSystem->Exec(), just like the standard C system() function, opens a new shell ("man system" says /bin/sh) with a brand new environment.
>>
>> But in ROOT you can set environment variables that are seen by subshells launched either via gSystem->Exec() or gSystem->OpenPipe()/GetFromPipe(): for instance you can play with the following code:
>>
>> // The environment variable COUNTER is set to 0
>> gSystem->Setenv("COUNTER", "0");
>>
>> // COUNTER is incremented in subshells and its value is set to ROOT's
>> // (*not* shell's) environment
>> for (Int_t i=0; i<100; i++) {
>> gSystem->Setenv("COUNTER", gSystem->GetFromPipe("expr $COUNTER + 1"));
>> }
>>
>> // A subshell is spawned to echo the value of envvar COUNTER
>> gSystem->Exec("echo Variable COUNTER has value $COUNTER");
>>
>> Please note that opening/closing 100 subshells just to increment a variable's value 100 times isn't very performance-friendly...
>>
>> Cheers,
>> --
>> : Dario Berzano
>> : INFN & Università - Torino, Italy
>> : Wiki: http://newton.ph.unito.it/~berzano
>> : GPG: http://newton.ph.unito.it/~berzano/gpg
>> : Mobile: +39 348 72 22 520
>>
>>
>> Le 9 mars 2011 à 11:53, Marc Escalier a écrit :
>>
>>

>>> Hello,
>>> 
>>> in root, there are the methods TSystem::Exec() and TSystem::GetFromPipe which have the same behaviour for the following issue :
>>> 
>>> if one does in unix :
>>> a=3
>>> echo $a
>>> it works
>>> 
>>> but in root :
>>> if ones does :
>>> gSystem->Exec("b=3);
>>> gSystem->Exec("echo $b")
>>> it will "forget" the b
>>> 
>>> only this works :
>>> gSystem->Exec("c=3;echo $c")
>>> 
>>> ==>
>>> is there a way to have the memory of the variables for several gSystem->Exec() commands ?
>>> (in order to do some instructions ones, and some others inside a loop)
>>> 
>>> (i tried also with export, but it doesn't help)
>>> 
>>> thanks
>>>    

>>
>>
>>

> Received on Wed Mar 09 2011 - 13:46:35 CET