Find problematic commit (removed something)

A)
#start bisect
$ git bisect start
#mark the commit you know is good
$ git bisect good fd0a623
#makr the commit you know is bad
$ git bisect bad 256d850


B)
#find string that was removed
$ git grep string_removed

# if not found, mark as bad
$ git bisect bad
# if found, mark as good
$ git bisect good

#repeat  step B until it shows first bad commit


#Once commit found, use reset to go back to original state
$ git bisect reset