Why does unix while read not read last line? [duplicate]

Answer 1

It is most likely due to absence of newline character after last line in your input file.

Run this command to find out:

cat -vte hello

And see what you get.

Answer 2

There exists a not very well-known, nasty hack to append a missing final newline to a text stream if and only if it's missing:

sed '$a\'

See this discussion on unix.stackexchange, for example.

Answer 3

This is an extensive reading for the question why?

If you don't want to put a new line at the end, you can do this:

while IFS=: read -r a b c d || [ -n "$a" ]; 
do     
echo $a,$b,$c,$d; 
done < file

Or using grep:

while IFS=: read -r a b c d; 
do     
echo $a,$b,$c,$d; 
done < <(grep "" filee)

Note:

1. There's no need to use cat with while loop.
2. You should almost always use the -r option with read.

Answer 4

What's happening is, the read command fails when the input is not terminated with a newline. Since the newline character is missing at the end of your file, the read fails, so the last iteration of the while loop is skipped.

If you don't want to / cannot make sure that your input file has a newline at the end, you can group your cat with an echo to give the appearance of an input terminated by newline, for example like this:

{ cat hello; echo; } | while read a b c d; do
    echo $a,$b,$c,$d
done

or like this:

(cat hello; echo) | while read a b c d; do
    echo $a,$b,$c,$d
done

Answer 5

Your file is probably missing a newline (\n) on the last line. You can prove this by printing the residual values of $a etc, like so

while IFS=: read a b c d; 
do     
echo $a,$b,$c,$d; 
done < hello  
echo $a,$b,$c,$d

Fix the file. Also, you should be able to set IFS specifically for the read as shown above. And no need to cat the file either, just use input redirection as shown