Read-while loop with 2-field tabulated data: cannot print second variable before first

Question

I have a 2-field csv file with the following values:

subID,Task
A,BLOCK
B,BLOCK
C,Finger

Reading via a read-while loop, if I print the two fields in order...

while IFS=',' read -r -a vars ; do
    echo ${vars[0]} ${vars[1]}
done < some.csv

 A BLOCK
 B BLOCK
 C Finger

But if I reverse the print order...

while IFS=',' read -r -a vars ; do
    echo ${vars[1]} ${vars[0]}
done < some.csv

  A
  B
  C

In fact, any text before ${vars[1]} will be ignored:

while IFS=',' read -r -a vars ; do
    echo foo bar ${vars[1]} ${vars[0]} foo bar
done < some.csv

  A foo bar
  B foo bar
  C foo bar

Just what is going on? Is BLOCK some sort of control character in bash?

For one, for that `read` to work, you need to have `IFS` contain the comma. Well, maybe you do. Maybe you do, but you're not showing it. Also the whitespace in the output is off. Which kinda leaves open the door that there might be something else in your script that you're also not showing but which might actually be relevant. — ilkkachu, Feb 10 '22 at 22:07
Anyway, use something like `cat -A some.csv` (or `cat -e`) to see if the file contains anything other than the printable characters, carriage returns or worse. — ilkkachu, Feb 10 '22 at 22:09
...there was a `^M` carriage return contained in the second field. Thanks for the clarification! — Zage12, Feb 10 '22 at 22:23
@Zage12, I wonder if you have a weird terminal, or something. Usually CRs just move the cursor back without clearing the line, so the text that comes after might only partially overwrite the text before. E.g. for the input line `A,BLOCK\r`, the second loop there prints `BLOCK\r A`, which on my terminal shows up as ` AOCK`. — ilkkachu, Feb 11 '22 at 07:58

0 Answers0