• My Ubuntu Perl shell doesn't have readline support

Installing the package libterm-readline-gnu-perl should get you readline support.

BTW, while looking up the exact package name (i.e. apt-cache search readline | grep perl), I accidentally also found perlconsole.  Maybe that's another one for you to try out...

$ apt-cache show perlconsole
...
Description: small program that lets you evaluate Perl code interactiv
+ely
 Perl Console is a light program that lets you evaluate Perl code
 interactively. It uses Readline for grabing input and provides comple
+tion
 with all the namespaces loaded during your session.
 .
 This is pretty useful for Perl developers that write modules.
 You can load a module in your session and test a function exported by
+ the
 module.
[download]

(I'm not a big fan of REPLs myself (prefer to have code in my editor), so I can't comment on its usefulness.)