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Full Discussion: Problem with pipes on infinite streams
Top Forums Shell Programming and Scripting Problem with pipes on infinite streams Post 302407979 by tokland on Saturday 27th of March 2010 12:04:56 PM
Old 03-27-2010
Problem with pipes on infinite streams
Here is an example code that shows the issue I have:

Code:
#!/bin/bash
counter() {
  seq 1000 | while read NUM; do
    echo $NUM
    echo "debug: $NUM" >&2 
    sleep 0.1 # slow it down so we know when this loop really ends
  done
}

counter | grep --line-buffered "[27]" | head -n1

Code:
debug: 1
debug: 2
2
debug: 3
debug: 4
debug: 5
debug: 6
debug: 7

If I understand it correctly, "head" finishes on the first match (as expected), but "grep" is not aware of it until it tries to write the next line (the second match). When it does, it finds out the pipe is closed so it also finishes.

That's normally not a problem, but if you have an infinite input stream containing only one match, it won't never stop. Any solution?
 

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HOCR(1) 							   User Commands							   HOCR(1)

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       --help-segmentation
	      Show segmentation options

       --help-debug
	      Show debug options

       File options

       -O, --images-out-path=PATH
	      use PATH for output images

       -u, --data-out=FILE
	      use FILE as output data file name

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	      save proccesd bw image

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	      font spacing: tight ..-1, 0, 1.. spaced

       Debug options

       -g, --draw-grid
	      draw grid on output images

       -d, --debug
	      print debuging information while running

       -D, --debug-extra
	      print extra debuging information

       -y, --font-filter=NUM
	      debug a font filter, use filter NUM

       -Y, --font-filter-list
	      print a list of debug a font filters

       -j, --font-num-out
	      print font numbers in output text

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	      use FILE as input image file name

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hocr - Hebrew OCR utility					   February 2008							   HOCR(1)
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