Understanding the output command


 
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# 1  
Old 01-12-2010
Understanding the output command

Could you please explain me whats happening in the below code, appreciate your help, Thank you.


Code:
/product/apps/informatica/v7/pc/ExtProc/NewDAC/dacRecBuilder.sh 
/product/apps/informatica/v7/pc/TgtFiles/NEW_DAC/DAC_Pos_TradeInv_Records.out 
/product/apps/informatica/v7/pc/TgtFiles/NEW_DAC/DAC_Pos_Gen.txt  
/product/apps/informatica/v7/pc/TgtFiles/NEW_DAC/DAC_Pos_TradeInvPositions.txt >
/product/apps/informatica/v7/pc/ScriptLogs/DAC_POS_TradeInv_Records.log 2>&1

# 2  
Old 01-12-2010
Quote:
Originally Posted by Ariean
Could you please explain me whats happening in the below code, appreciate your help, Thank you.


Code:
/product/apps/informatica/v7/pc/ExtProc/NewDAC/dacRecBuilder.sh \
        /product/apps/informatica/v7/pc/TgtFiles/NEW_DAC/DAC_Pos_TradeInv_Records.out \
        /product/apps/informatica/v7/pc/TgtFiles/NEW_DAC/DAC_Pos_Gen.txt \
        /product/apps/informatica/v7/pc/TgtFiles/NEW_DAC/DAC_Pos_TradeInvPositions.txt \
        > /product/apps/informatica/v7/pc/ScriptLogs/DAC_POS_TradeInv_Records.log 2>&1

That looks like one big line that's been wrapped across multiple lines. I've added backslashes and indentation to make it more apparent. It runs dacRedBuilder.sh, giving it several filenames as parameters, redirecting its standard output to a file(highlighted in red), and redirecting its standard error into standard output(blue).

What the script actually does to all those files, I have no idea. I can't read the script from here. Smilie
# 3  
Old 01-12-2010
Thanks for your reply, okay my understanding from your comments is that the output of the shell script would be written to a file and when you say "standard output(blue)." does you mean to say that it would print the same content on the putty screen also when you execute the script in putty apart from the creation of output file??

Thanks,
Ariean
# 4  
Old 01-13-2010
Quote:
Originally Posted by Ariean
Thanks for your reply, okay my understanding from your comments is that the output of the shell script would be written to a file and when you say "standard output(blue)." does you mean to say that it would print the same content on the putty screen also when you execute the script in putty apart from the creation of output file??

Thanks,
Ariean
No, standard output is by default to screen. But here it is redirected to the file: DAC_POS_TradeInv_Records.log , also the standard error is also redirected to same file, so you will not get anything printed in the screen.
# 5  
Old 01-13-2010
I am missing something what do u mean by standard error? i understand standard output is the output printed on screen when i execute the script. But i didn't understand "2>&1" part, whats happening over there?

Thanks,
Ariean
# 6  
Old 01-13-2010
Quote:
Originally Posted by Ariean
I am missing something what do u mean by standard error? i understand standard output is the output printed on screen when i execute the script. But i didn't understand "2>&1" part, whats happening over there?

Thanks,
Ariean
By tradition, a UNIX process has three default streams: standard input(stdin), standard output(stdout), and standard error(stderr). stdin is represents the terminal keyboard as file descriptor 0, stdout represents the terminal screen as file descriptor 1, and stderr is also directed to the terminal screen as file descriptor 2.

The idea with having two files going to the terminal is to keep data and error messages separate. You can redirect the data output of a process into a file and still see human-readable error messages on your terminal. It also helps keep error messages OUT of data files since other programs probably won't need or understand them.

Here they're redirecting both stdout and stderr into the data file, for better or for worse. The "2>&1" bit tells it to redirect FD 2, stderr, to the same destination as FD 1, stdout.
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