sed in-place editing gotcha in OS X

I just started learning about sed and came across one "gotcha" when using the -i option in OS X. The -i option allows you to edit a file in-place. It takes an optional parameter - a string to use as the extension for the backup file. If this parameter is not provided, then a backup file is not created.

I was using sed to remove some tag references from a ctags file. Since the file could easily be re-generated I didn't feel the need to provide a backup extension. I tried to execute the command below, but received an error:

→ sed -i "/lib\/timekeeper\/employee.rb/d" tags 
sed: 1: "tags": undefined label 'ags'

After some head scratching and Googling I figured out that in OS X the parameter is not optional, so the correct command is this:

→ sed -i "" "/lib\/timekeeper\/employee.rb/d" tags