How to format the Rspec output? or write output on to a file?

Rspec supports various types of output formats like Html, Progress/Txt and Progress. You can use any one of them or all of them once

Add the following lines to your .rspec file:

--format progress 
--format documentation -o "output/result.log"
--format html -o "output/result.html"

--format specifies the type of output format and -o tag is used to write the output to a specified file