porjo

# Look for instantiations of error using fmt.Errorf or errors.New, where first letter is upper-case. Convert that letter to lowercase.
# e.g. 
#   return fmt.Errorf("User...
#   return errors.New("User...
# becomes
#   return fmt.Errorf("user...
#   return errors.New("user...

find -name '*.go' -exec sed 's/\(\(errors\.New\|fmt\.Errorf\)("\)\([A-Z]\)\(.*\)/\1\l\3\4/' {} \;