invalid command code ., despite escaping periods, using sed

If you are on a OS X, this probably has nothing to do with the sed command. On the OSX version of sed, the -i option expects an extension argument so your command is actually parsed as the extension argument and the file path is interpreted as the command code.

Try adding the -e argument explicitly and giving '' as argument to -i:

find ./ -type f -exec sed -i '' -e "s/192.168.20.1/new.domain.com/" {} \;

See this.

You simply forgot to supply an argument to -i. Just change -i to -i ''.

Of course that means you don't want your files to be backed up; otherwise supply your extension of choice, like -i .bak.

On OS X nothing helps poor builtin sed to become adequate. The solution is:

brew install gnu-sed

And then use gsed instead of sed, which will just work as expected.