By my read, it prints a list of all Ruby files in your project sorted by number of commits against them. It may take a long time to complete depending on number of files and number of commits.
Actually, it finds all Ruby .rb files, then prints out that file every time a change was made to the file. It then does a count of each of the times the file is output, and then sorts the list with those files that were modified the most frequently being at the top, and those modified least frequently being at the bottom.
In other words, it shows (as the poster says) file churn in a Ruby codebase.
YMMV, I am not a BASH shell.