Find all files with the extension ".csv" and execute a command to replace any numbers in the format "###-###-####" with the format "(###) ###-####" for each file.
find -name "*.csv" -exec sed -i '' 's/[0-9]\{3\}-[0-9]\{3\}-[0-9]\{4\}/\([0-9]\{3\}\) [0-9]\{3\}\-[0-9]\{4\}/' {} \;