[GRASS5] Re: stdout and stderr

[Stefan Paulick]

I would appreciate to have some kind of dynamic configureable dispatcher, 
redirecting outputs to different targets. 


Mit freundlichen Grüßen / With kindest regards 


Stefan Paulick 


stefan.paulick at urbeli.com
http://www.urbeli.com
/*----------------------*/ 

Paul Kelly schrieb: 

> Hello developers
> I was just wondering about the appropriateness of writing different types 
> of module output to stderr or stdout, as I notice there has been some 
> activity in 5.7 in this area recently. I am wondering if perhaps I have 
> been wrong about how this should be used before: 
> 
> When writing new code and fixing bugs I have tended to ensure that only 
> output which is the actual result of a GIS processing operation that needs 
> to be displayed to the user (rather than written to a file in the GRASS 
> database) should be written to stdout. All other errors, warnings, 
> informative progress messages and copyright notices etc. are written to 
> stderr. 
> 
> I'll use the example of re-directing output to a file to show why this 
> makes logical sense to me.
> g.proj -wf proj4=+init=epsg:29900 > irishgrid.prj
> The point of this command is to convert the projection description 
> described by '+init=epsg:29900' in PROJ.4 format into WKT format and store 
> it in a .prj file. The WKT output is printed to stdout and stdout 
> re-directed to a file, which accomplishes this nicely. But on running the 
> above command, it is determined that +init=epsg:29900 does not contain 
> enough information on datum parameters, so the user is prompted for more 
> information. These prompts are written to stderr, so the user can still 
> see them even though stdout is re-directed. The user can interactively 
> choose the datum paramters and then the final version of the WKT output is 
> written to the file. If the prompts also went to stdout then the user 
> wouldn't see them and the program would just hang waiting for input from 
> the user. 
> 
> I suppose that for modules that only write output to another file in the 
> GIS database, having information messages printed to stdout wouldn't 
> result in mixing up, but still I was under the (possibly mistaken) 
> impression that writing to stderr ensured the messages would always appear 
> where the user could see them and act on them, regardless of where stdout 
> was appearing (e.g. in a future GUI perhaps the stdout would be placed in 
> a pretty 'results' window to be stored while stderr could be kept out of 
> the way). 
> 
> Any thoughts? 
> 
> Paul 
> 
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