This is a command-line utility that counts the number of duplicate lines in your streamed input.
Quite plainly, this is the command line equivalent of this Duplicates in a List Online Tool by Shailesh N. Humbad.
npm i -g wvbe/count-duplicate-lines
Pipe your lines into this sucker like:
cat lines.txt | count-duplicate-lines
--porcelain will send a line- and tab-separated value table, instead of something more readable.