How to iterate on different lists according to a parameter - bash

Question

I have a script that can get a list of folders or get them automatically with find. I'd like to write a single loop that handles both cases: if there are parameters, use them, otherwise, create the list automatically.
So far, I have something like:
if [ "$#" -gt 0 ]
then
for value in "$#"
do
v1=$(process_data "$value")
<do things with $v1>
done
else
for value in "$(find ...)"
do
v1=$(process_data "$value")
<do things with $v1>
done
fi
I'd like to do something like:
if [ "$#" -gt 0 ]
then
data="$#"
else
data="$(find ...)"
fi
for value in "${data[#]}"
do
v1=$(process_data "$value")
<do things with $v1>
done
but this data assignment can be potentially big. In a language with pointers this should not be a problem, but in bash it doesn't look good.
Is there a better way to achieve my needs?

Answer 1

These don't look right:
data="$#"
data="$(find ...)"
If you want data to be an array, you need
data=("$#")
data=($(find ...))
What you can do is assign to the positional parameters:
#!/bin/bash
if [ "$#" = 0 ]
then
# no arguments; default to all matching files
set -- $(find ...)
fi
for value in "$#"
do
# things
done
This does mean that the loop can't start until the find command finishes. To solve that, an alternative might be to turn it around and make using "$#" more like the output of find, i.e. stream it to a pipe, like this:
#!/bin/bash
args_or_find() {
if [ "$#" -gt 0 ]
then
printf '%s\n' "$#"
else
find ...
fi
}
while read -r value
do
# things
done < <(args_or_find)
The natural extension to improve robustness using \0 instead of \n as separator is left as an exercise.

Answer 2

You may use a script like this to have processing loop only once:
if (($#)); then # arguments are passed
arr=("$#")
else # build array from find command's result
arr=()
while IFS= read -rd '' f; do
arr+=("$f")
done < <(find . -name '*.txt' -print0)
fi
# main processing loop
for line in "${arr[#]}"; do
echo "processing... <$line>"
done