[GRASS-dev] Re: [GRASSLIST:962] Re: GRASS and vector lines: how can I change the direction of digitized lines?

[Maciek Sieczka]

Guys,

I really read all I could on the net and nowhere I found an explanation
why would

$ v.patch input=cieki04,cieki05 output=cieki06 >&1> /dev/null
as well as
$ v.patch input=cieki04,cieki05 output=cieki06 >&2> /dev/null

result in the output being reduced to:

 [1]

> Patching file cieki04
> Patching file cieki05
> Patch complete. 2 files patched.
> Intersections at borders will have to be snapped.
> Lines common between files will have to be edited.
> The header information also may have to be edited.

instead of a much more verbose, when v.patch is called normally:

 [2]

> Patching file cieki04
> Patching file cieki05
> Building topology ...
> 372 primitives registered
> Building areas:  100%
> 0 areas built
> 0 isles built
> Attaching islands:
> Attaching centroids:  100%
> Topology was built.
> Number of nodes     :   207
> Number of primitives:   372
> Number of points    :   0
> Number of lines     :   372
> Number of boundaries:   0
> Number of centroids :   0
> Number of areas     :   0
> Number of isles     :   0
> Patch complete. 2 files patched.
> Intersections at borders will have to be snapped.
> Lines common between files will have to be edited.
> The header information also may have to be edited.



Needless to say, as normal "> /dev/null" doesn't any help in case of
v.patch and v.clean output, I like [1] more than [2] and would like to
use ">&1> /dev/null" in my script to reduce v.patch and v.clean
verbosity, while leaving them able to issue warnings and errors still.

On the other hand, since I really don't understand why/how it works, I
don't want to cause any troubles to other eventuall users of my script,
in case it turns out be not portable/buggy/else in circumstances I
don't realize.

Could anybody knowledgable tell me if redirecting like ">&1> /dev/null"
is any wrong? Moreover, how it works anyway? I just tried it by luck
and it turned out to produce a nice result, that's all I know.

Looking forward to any hints from you.

Maciek

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