Suppose I have a list of URLs in a text file:

 google.com/funny
 unix.stackexchange.com/questions
 isuckatunix.com/ireallydo

I want to delete everything that comes after '.com'.

Expected Results:

 google.com
 unix.stackexchange.com
 isuckatunix.com

I tried

 sed 's/.com*//' file.txt 

but it deleted `.com` as well.