It’s not a typo. The first section of the regex is a matching section, where a dot means “match any character”, and an escaped dot is a literal dot character. The second section is the replacement section, and you don’t have to escape the dot there because that section isn’t matching anything. You can escape it though if it makes the code easier to read.

rename is written in Perl so all Perl regular expression syntaxes are valid.

However, your comment did make me realize that I hadn’t escaped a dot in the third example! So I fixed that.