Shell Programming and Scripting

HI all,

I want to capture cpu data in batch mode of "top" command and redirect to a file like this:

Code:

top -b > cpu.dat

it works!
But I want to capture only Cpu lines, so i have:

Code:

top -b | grep ^Cpu >cpu.dat

Then I got an empty output file.
Why?
Could somebody explain and help me to make it work.
Thanks

Hard to explain if we do not know input data.
Anyway - 'grep ^Cpu' should work. Empty output file tells only that there are no lines with word "Cpu" on the beggining of a line.

hi,
the direct answer for your 'why' is
->the output is not going to std out it is going to std err


secondly how to accomplish it
->method 1
$top 2>outputOfTop
or
$top >& outputOfTop

then
$grep pattern outputOfTop

->method 2
open two terminal term1 and term2

in term1
$mkfifo pipe
$top 2>pipe

in term2
$grep pattern pipe

make sure the working directory is same in both the terminal
i hope this should work

Best Regards,
Rakesh UV

uvrakesh: if "top -b >cpu.dat" worked then the output was not being written to stderr.

My copy of top (Ubuntu Linux 7.10) writes to stdout. But it keeps on looping even with the -b option, so I don't have exactly the same version.

fongthai: if top -b >cpu.dat works then does grep ^Cpu cpu.dat work? That would be a workaround at least.

top -b | grep ^Cpu output is sure no error, it output should be like this:

"Cpu(s): 1.7%us, 0.8%sy, 0.0%ni, 96.9%id, 0.5%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu(s): 0.0%us, 1.3%sy, 0.0%ni, 98.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st"

i should go to stdout. I think.

I tried your methods but they don't work.
Any other idea?

Repeat: do you get these lines in the file when you do top -b >cpu.dat?

Yes, I got them.
I don't want to get data first then using grep, because it make output file become a huge file. I want to run top -b for one or two days, that's the issue.