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I was trying to read a file line by line(each line is a hostname), do some processing like this : 

while read -r line
do 
  if ping -c1 $line
     echo $line is running  
  fi 
done <file.txt

I found that the out put is like this: 

  is running
  is running 
  ...

As if the variable $line is empty.

Thanks to all who commented this question. I think I now understand what happened.

So the file has CRLF line ending. And the length of a line is exactly the same as is running.

Because of the CR character at the end of $line, the content of $line gets completely overwritten by is running. If only the length of a line is longer, I would have asked the question differently.

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10
  • What is the contents of the file? Does $line start with a dash (-)? What if you use printf '%s is ok' "$line"? Commented Jun 8, 2018 at 6:55
  • Does file.txt have Window-style (CRLF) line endings? Commented Jun 8, 2018 at 6:55
  • if I add a echo $line after fi, aka outside of the if block, it would work perfectly. The text file contains a list of hostnames, lines don't start with dash. I'm sure the content can be read ok as echo outside of the if works. Commented Jun 8, 2018 at 7:01
  • @steeldriver yes I think it has CRLF line endings Commented Jun 8, 2018 at 7:10
  • 1
    You have now edited the code in the question so that the text no longer matches up with it. Please edit it again so that we can see what code you are actually running. Commented Jun 8, 2018 at 7:18

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