The output of the command below is weird to me. Why does it not give me back element 5?
$ echo '0,1,2,3,4,5' | while read -d, i; do echo $i; done
0
1
2
3
4
I would expect '5' to be returned as well. Running GNU bash, version 4.2.46(2)-release (x86_64-redhat-linux-gnu). Adding a comma works, but my input data does not have a comma. Am I missing something?
With read, -d is used to terminate the input lines (i.e. not to separate input lines). Your last "line" contains no terminator, so read returns false on EOF and the loop exits (even though the final value was read).
echo '0,1,2,3,4,5' | { while read -d, i; do echo "$i"; done; echo "last value=$i"; }
(Even with -d, read also uses $IFS, absorbing whitespace including the trailing \n on the final value that would appear using other methods such as readarray)
The Bash FAQ discusses this, and how to handle various similar cases:
As other answers state, -d is an end-of-line character, not a field separator. You can do
IFS=, read -a fields <<< "1,2,3,4,5"
for i in "${fields[@]}"; do echo "$i"; done
From man:
-d delim
The first character of delim is used to terminate the input line, rather than newline.
Your element 5 doesn't have a delimiter (comma), so it won't be read.
What you're seeing is the same behavior (and for the same reason) as Why does this 'while' loop not recognize the last line?
As in that case, you can modify the behavior by adding an extra test to the loop termination condition, as follows
while read -d, i || [[ -n $i ]]; do ...
Ex.
$ echo '0,1,2,3,4,5' | while read -d, i || [[ -n $i ]]; do echo $i; done
0
1
2
3
4
5
read -d, i || [[ -n $i ]]a la What doeswhile read -r line || [[ -n $line ]]mean? – steeldriver May 17 '19 at 11:18