http://www.perlmonks.org?node_id=884273


in reply to Stupid mistakes I repeatedly make

s/// at the end of a map()
Me too. And I'll probably continue to do it even after perl 5.14 is released. The new /r modifier was introduced in perl 5.13.2 perlop:
If the /r (non-destructive) option is used then it will perform the substitution on a copy of the string and return the copy whether or not a substitution occurred. The original string will always remain unchanged in this case. The copy will always be a plain string, even If the input is an object or a tied variable.
@foo = map { s/this/that/r } @bar # /r is very useful in maps