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Thread: Drop special character from piped value

  1. #1
    Join Date
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    Drop special character from piped value

    I'm trying to drop the character ^M from my piped command, however, I can't seem to get it to drop.

    In one terminal window, I am running
    Code:
    echo -en "adc read 0\r"  > /dev/ttyACM0
    which makes my device send back some results with numbers to the same port. To read the returned value, I am in a separate window I am running
    Code:
    cat -v < /dev/ttyACM0 | grep -v ">"
    function that is already cleaning up some of the results, but still allowing ^M to come back. I have tried dropping all but numbers by expanding my cat to
    Code:
    cat -v < /dev/ttyACM0 | grep -v ">" | tr -dc '[:alnum:]'
    , but no luck.

    I'm open to ideas on how to drop the two characters that I don't want to see.
    Last edited by Superdude_123; September 6th, 2017 at 11:53 PM. Reason: Add tags

  2. #2
    Join Date
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    Re: Drop special character from piped value

    Simply
    Code:
    cat -v < /dev/ttyACM0 | grep -v ">" | tr -d '\r'
    will drop the carriage returns. Which other character are you wanting to drop?

  3. #3
    Join Date
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    Re: Drop special character from piped value

    That just got me some blank results.

    If I wanted to filter the character ^ and the letter M out, how could that be done?

  4. #4
    Join Date
    Apr 2012
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    Re: Drop special character from piped value

    If you don't want carriage returns to be displayed as ^M, don't add the -v to the cat

    Code:
    cat < /dev/ttyACM0 | grep -v ">" | tr -d '\r'
    If you want to keep the -v for some reason, then you will need to treat ^M as literal characters e.g.

    Code:
    cat -v < /dev/ttyACM0 | grep -v ">" | sed 's/\^M$//'

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