When executing a perl search and replace on the command line, how do I lower case a matched token?

Question

I have a file with lines like

TEST=value

I would like to do a search and replace such that I replace the first token with its lower case equivalent. So the above would be transformed into

prefix/test —output value

I tried the below

perl -pi -e ’s/(.*)=(.*)/prefix\/lc($1) —output $2/g' .env

But evidently “lc” is being interpreted literally because the result is

prefix/lc(TEST) —output value