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Old 12-01-2010, 08:48 AM   #1
mwilner
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Redirecting output from stderr


I have seen a post where someone was explaining the virtuality of stdout and stderr and that it can be redirected with e.g. 2>file.txt but this apparently is not working for me!
I have a CUPS filter with fprintf(stderr,...) statements but don't know how to make these visible to me.

Can someone help me get the idea?

Thank you,
\Manfred
 
Old 12-01-2010, 09:16 AM   #2
grail
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You may need to put a little more out there than a reference to something which may or may not be the problem.
Display the filter you are using and I am sure someone will have some advice
 
Old 12-01-2010, 11:33 AM   #3
emmalg
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I agree, there isn't really enough information here to provide a detailed response, however to give an equally vague response which may or may not help, stdout is "1" and stderr is "2" (stdin is 0).

So if you want to redirect the output of a command to a file you may write:

Code:
command > outfile.txt
To redirect only the stderr to a file you write:

Code:
command 2> outerr.txt
to redirect your standard error to the same file as your standard output:

Code:
command > outfile_and_error.txt 2>&1
Be aware though, if you use the last method, particularly for debugging, that stdout and stderr aren't synchronised. Your error message may turn up several lines earlier than the stdout messages when you think the programme should have failed.

If you run a google search for stdout stderr you should be able to find more information quite easily.

Also make sure that the output isn't being redirected to /dev/null anywhere.

Emma
 
Old 12-01-2010, 12:59 PM   #4
mwilner
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Ok, thanks for the advice about detail.
I am writing/debugging a CUPS filter that has fprintf(stderr...) statements to show at various states the values of variables.
When I am printing I expect these fprintf's to be hit and send the output to stderr.
While I am not sure where stderr has been redirected to /dev/null I am assuming it has since I don't see anything anywhere.
My question now is there a program or way to read these stderr outputs?

If I just redirect as described below inside a terminal it still doesn't catch the output from the CUPS filter while printing.
 
Old 12-01-2010, 01:30 PM   #5
emmalg
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Ah ok. I'm beginning to see through the fog... :-)

Check the following link out which might give an indication as to why it isn't working and a possible solution:

http://lists.apple.com/archives/prin.../msg00004.html

A quick internet search using CUPS filter fprintf stderr gave a few results and a short glance through suggests that stderr from a filter will not be seen.

As I'm not sure what you're up to exactly I don't think I can offer any more help.

Cheers!
 
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Old 12-02-2010, 08:25 AM   #6
mwilner
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Thank you emmalg this will guide me in my development.
\Manfred
 
  


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