Working with a directories of unknown files

Using http://mywiki.wooledge.org/BashFAQ/020 as a starting point, you could:

find /tmp -type f -print0 | while IFS= read -r -d '' file
do
   echo properly escaped "$file" for doing stuff
done

However that’s a bit ugly. And note that -d '' only works in bash. So none of this is “POSIX”.

Another way of writing this, which works from bash 4 is using dotglob/globstar:

shopt -s dotglob  # find .FILES
shopt -s globstar # make ** recurse
for f in /tmp/**
do
	if [[ -f $f && ! -L $f ]]
	then
		echo properly escaped "$f" for doing stuff
	fi
done

Another perhaps more POSIX way is

foo () { for i in "$@"; do echo $i; done };export -f foo;find /tmp -type f -exec bash -c 'foo "$@"' - {} + | wc -l

I.e. export a script function to be executed by the -exec parameter of find, or just use a seperate script file.