iwc(1) is an interactive wc(1). It mostly works like the original wc but prints the lines number as it counts them instead of waiting for the end to print it.

brew install bfontaine/utils/iwc

git clone https://github.com/bfontaine/iwc.git && cd iwc
git checkout v0.1.3  # last stable version
[sudo] make install

$ iwc myfile.txt

See the man page for all available options.

You can combine iwc with tail -f to follow the number of lines in a file that’s constantly growing (like logs):

$ tail -f -n +1 your_file | iwc -l

MIT