problems with read in bash script

Question

I am trying to read line by line from a serial port. The code below works, but I keep getting an error which I do not understand. Any clue?

That's the code

    while read line ; do
    if [ "$(line)"=='OFF' ] ;
      then
         echo "that was actually OFF"
    fi
    done < /dev/ttyACM0

That's the error:

   that was actually OFF 
   ./reading_loop.sh: line 9: line: command not found

@ssdecontrol: because it was so short. But you're right, it was actually an answer — Ronald
– Ronald, Commented Aug 30, 2014 at 11:23

glenn jackman · Accepted Answer · 2014-08-29 12:08:14Z

1

if [ "$(line)"=='OFF' ] ;

$(...) executes the contents of the parentheses and returns the stdout. If you don't have a command named line you'll see a "command not found" error message, and $() will return an empty string.
[...] does different actions based on the number of arguments given. Since you only give a single word, the [ command merely checks if the string is empty or not. In this case, [ will see ""=='OFF' which is not empty, therefore the success block will always be executed.

answered Aug 29, 2014 at 12:08

glenn jackman

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