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no data redirected to a file with top and grep - why?

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Top Forums Shell Programming and Scripting no data redirected to a file with top and grep - why?
# 8  
Old 04-24-2008
If you run it without redirection, do you see the results on your screen?

If you terminate it with ctrl-c, the output might still be buffered somewhere (weak hunch, might be wrong) -- if you let it run for long enough, does the output become visible?
# 9  
Old 04-24-2008
era,

top -b will run looping, of course. I will use, for example: "top -b -d 10" it will refresh every 10 seconds.
# 10  
Old 04-24-2008
Tested here; looks like I'm right. If I hit ctrl-c after five seconds (enough to produce about two matching lines, I guess) the output file is empty. If I run it for a minute or so, I still don't get output in the file. Then all of a sudden, lots of output. It's output buffering at play.

If you have grep --line-buffered, try with that, just to see that it works. If you run it for long enough, you probably want to take it out again, though.
# 11  
Old 04-24-2008
@era: Yes, I can see the result on the screen without redirection.
I left it run for half a day (without grep), and kill it, I got the output with over 200MB
# 12  
Old 04-24-2008
era, have you got any solution for it?
# 13  
Old 04-24-2008
Scroll back and read?
# 14  
Old 04-24-2008
You answer:
Quote:
Originally Posted by era
fongthai: if top -b >cpu.dat works then does grep ^Cpu cpu.dat work? That would be a workaround at least.
But I still keep the idea of using grep then redirect to file.

My feedback:
Quote:
Originally Posted by fongthai
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.
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