How to keep backslash when reading from a file?

Question

When I use "cat test.file", it will show

printf "This is a test log %d \n, testid";
 1
  2

When I use the bash file,

IFS=""
while read data
do
    echo "$data"
done << test.file

It will show

printf "This is a test log %d n, testid";
 1
  2

The "\" is gone.

Is there any way that I can keep the "\" and space at the same time?

Answer 1

Try using read -r.

From the man page:

-r
If this option is given, backslash does not act as an escape character. The backslash is considered to be part of the line. In particular, a backslash-newline pair may not be used as a line continuation.

Execute this to test it:

read -r a < <(echo "test \n test"); echo $a