'find' template for handling any file
This code is vulnerable to TOCTOU. There is a tiny gap between the time that "plain files" are read from the process substitution (find -type f ...) and the time that readlink(1) is called on those filenames.

An attacker could create a program that waits for your program to run and then quickly deletes one of those files found by find(1) and replaces it with a symlink to somewhere else. readlink(1) will then dutifully return the target of that symlink and this is the path that will be output. The target could be outside $absolute_dir_path and a file of any type (directory, device node, ...).

Eg:

#!/bin/bash

set -o errexit
set -o nounset
set -o noclobber

# setup directory containing two plain files
# hardcode absolute_dir_path to /tmp/dir for simplicity
mkdir -p /tmp/dir
rm -f /tmp/dir/a /tmp/dir/b
touch /tmp/dir/a /tmp/dir/b

# emulate OP's find loop, but with inserted actions
# performed by an attacker (in real attack these would
# happen in an external program).
exec 9&lt; &lt;( find /tmp/dir -type f -print0 )
while IFS= read -r -d '' -u 9
do
        file_path_x="$(readlink -fn -- "$REPLY"; echo x)"
        file_path="${file_path_x%x}"
        ls -l "${file_path}"
        # attacker jumps in here and does:
        rm /tmp/dir/b
        ln -s /etc/passwd /tmp/dir/b
done


Output:

-rw-r--r-- 1 martin martin 0 2011-03-31 10:56 /tmp/dir/a
-rw-r--r-- 1 root root 2119 2011-03-28 11:35 /etc/passwd


The risk can be mitigated by only seeking files in directories beneath which untrusted users do not have write access. Directories such as /tmp and /var/tmp are problematic though and this is hard to solve. See the source of (eg) tmpreaper for some ideas.