When ctl-D is entered the value assigned to the variable ans is null. In this case, the if evaluates true because <nul>X is the same as Xand thus the loop is broken.

This is an alternative:

Code:

#!/usr/bin/env ksh
count=0
printf ">"
while read line
do
        printf ">"
        count=$((count+1))
done
echo "read $count lines"
exit

While will read from standard input until the end of the file and exit the loop without an explicit test. The only "odd" thing is the need to issue a prompt before the loop.