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 Forum index » Off-Topic Area » Programming
What's the difference in these two lines of code?
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RSH


Joined: 05 Sep 2011
Posts: 1564
Location: Germany
PostPosted: Sat 12 Jan 2013, 00:32    Post subject:  What's the difference in these two lines of code?  
Hi.

I hope anyone can tell me what is the difference (in functionality) between the two following code lines:
Code:
cp -af /root/puppy-reference /tmp/root/

Code:
cp -af /root/puppy-reference /tmp/root/ 2>/dev/null

Thanks

RSH
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sunburnt


Joined: 08 Jun 2005
Posts: 4006
Location: Arizona, U.S.A.
PostPosted: Sat 12 Jan 2013, 01:09    Post subject:  
Hi RSH; 2> redirects the error output of the command.
/dev/null is a "black hole" that swallows whatever is sent to it.

Code from my AppPkg mount file:
Code:
Etc=`find etc/* 2> /dev/null`

If there`s no etc dir. in the current dir., there`s no error output in a VT.
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matiasbatero


Joined: 11 Oct 2012
Posts: 13
Location: Mar del Plata, Argentina
PostPosted: Sat 12 Jan 2013, 12:39    Post subject:  
2> /dev/null is very usefull when you wants to make a silent scripts.
Adding 2> /dev/null, you send the ouput error to the trash, and nothing is printed on your screen.
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don570


Joined: 10 Mar 2010
Posts: 2465
Location: Ontario
PostPosted: Sat 12 Jan 2013, 14:57    Post subject:  
Code:

cp -af /root/puppy-reference /tmp/root/  2>/tmp/error$$


I have found that funnelling the error
message to a file in /tmp is useful in studying whether
my partition is filled up. I do a 'grep' of /tmp/error$$
to see if there is text 'no space left' or whatever that error message is.


I used that technique in my pet packages 'Extract-pet' and 'Extract-debian'
to warn the user that there is not enough disk space to do extraction.

It works well with 'mv' command or 'mv -i' command I believe.

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postfs1


Joined: 27 Mar 2010
Posts: 831
PostPosted: Sat 12 Jan 2013, 15:08    Post subject:  
Maybe: request for a third-party programmatic option.
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sunburnt


Joined: 08 Jun 2005
Posts: 4006
Location: Arizona, U.S.A.
PostPosted: Sat 12 Jan 2013, 23:31    Post subject:  
I`ve always thought that copy and move should check target free space.
What`s the point in even beginning to copy if there`s not enough space?

Remembering the days of copying to a floppy only to have it fail at the end
because the darn thing has enough bad sectors that it won`t hold the data.
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RSH


Joined: 05 Sep 2011
Posts: 1564
Location: Germany
PostPosted: Sun 13 Jan 2013, 00:52    Post subject:  
Hi.

Thanks to all for clearing this. I was a bit afraid to have left something out that would be necessary - in all of my programs. Laughing

RSH
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