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View Full Version : [ubuntu] pipes and redirection subtlety with awk



floobit
April 9th, 2012, 02:50 PM
I'm not sure where to put this thread, as it's mostly just about pipes and redirection. I am trying to write iostat statistics to a log file, so do something like this:


iostat sda 2 > today.log

But this gives me lots of unwanted text. I could clean up the log file, but it would be quicker to use awk. This line gives me exactly the numbers I want, printed onto the screen (user CPU and CPU spent waiting for IO):


iostat sda 2| awk 'NR%6==4{print $1 " " $4}'

Unfortunately, this line creates a file with no contents:


iostat sda 2| awk 'NR%6==4{print $1 " " $4}' > today.log

Why?