Bash variable substitution on find's output through exec

Question

Is there any way to apply Bash variable substitution on find's output? I know I've seen someone do it on Stack Overflow but I can't seem to find that particular post anymore.

As an example, let's say I want to rename files ending in *.png to *_copy.png. I know I can do this using rename but it's just a thought experiment.

Now I'd like to be able to do something like this:

find . -name "*png" -exec mv "{}" "${{}%.*}_copy.png" \;

Which results in an invalid substitution. Of course, I could first assign the output to a variable and then apply substitution in a sub-shell, but is this really the only way?

find . -name "*.png" -exec bash -c 'var="{}";  mv "{}" "${var%.*}_copy.png"' \;

Or is there any way this can be achieved directly from {}?

Consensus

As Etan Reisner remarked, a better and safer way to handle the output of find would be to pass it as a positional argument:

find . -name "*.png" -exec bash -c 'mv "$0" "${0%.*}_copy.png"' "{}" \;

Answer 1

It took me a while to get the question. Basically you are asking if something like:

echo "${test.png%.png}"

could be used to get the word test.

The answer is no. The string manipulation operators starting with ${ are a subset of the parameter substitution operators. They work only on variables, not with string literals, meaning you need to store the string in a variable before. Like this:

img="test.png"
echo "${img%.png}"

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Just for travellers from Google, I would use rename for this particular task. (As the OP already mentioned in his question). The command could look like this:

find -name '*png' -execdir rename 's/\.png/_copy.png/' {} +