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I would like to parse the output of cdrecord/wodim using grep. cdrecord -v outputs lines like

Track 01:   49 of   75 MB written (fifo 100%) [buf 100%]  10.2x.

The problem is that cdrecord uses carriage returns (CR, \r) in order to show the progress in the same line.

I tried to append tr '\r' '\n' to the cdrecord call, which works generally, but the output won't show line by line. Instead, large chunks of text are parsed and displayed:

cdrecord -v ... | tr '\r' '\n' | grep -i written

Is this due to cdrecord, tr or grep? Is there any way to force flushing in order to get the output line by line?

Any help appreciated.

  • 2
    IIRC tr and grep both are buffered..you can try cdrecord -v ... | stdbuf -o0 tr '\r' '\n' | grep --line-buffered -i written – heemayl Feb 10 '16 at 13:23
  • @heemayl: thank you very much! Works like a charm! However, the --line-buffered option of grep only works on grep's output, so I guess this is unnecessary. – mefiX Feb 10 '16 at 13:48
  • Right.. Answer added.. – heemayl Feb 10 '16 at 13:51
  • Important here is that cdrecord calls fflush(stdout) to update a line. This is sufficient for all GUI implementations that parse the output in order to convert it into a growing bar window. – schily Feb 10 '16 at 14:57
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The output of tr is buffered. You can use stdbuf -o0 with tr to make it's STDOUT unbuffered:

cdrecord -v ... | stdbuf -o0 tr '\r' '\n' | grep -i written

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