Put complete names in the file like a relative path from a starting directory.

Code:

./path/to/fname

Or a full path

Code:

/directory/path/to/fname

This is efficient in that it invokes tar once. And simply writes to the current end of the tar file. The tarfile must exist for this work.

Code:

my_tar=/tmp/mytar.tar
touch $my_tar                      # create the file if needed
cd /starting/directory
tar -rvf $my_tar `cat /path/to/list_of_files.txt`

tar usually has a -u option (update). Try to avoid it, because it is sloooow. -r is a simpler way to keep the most recent copy of a file.

Let's say you want files just modified in the last 24 hours, here all put together.

Code:

cd /starting/directory
find . -mtime -1 > /path/to/list_of_files.txt
my_tar=/tmp/mytar.tar
touch $my_tar                      # create the file if needed
tar -rvf $my_tar `cat /path/to/list_of_files.txt`