# perl -e "\$_='qwerty';s/r/print pos();/e;"
3

BUT

# perl -e "$_='qwerty';s/r/print pos();/e;"
syntax error at -e line 1, near ";="
Execution of -e aborted due to compilation errors.

# uname -v
Darwin Kernel Version 10.4.0: Fri Apr 23 18:28:53 PDT 2010; root:xnu-1504.7.4~1/RELEASE_I386