The portable way to handle versions is with the version module. In this case you just want the default stringification of the version object:

  zen% /opt/bleadperl/bin/perl -Mversion -wle 'print version->new($])'
  5.9.2
  zen% /opt/perl5.005_03/bin/perl -Mversion -wle 'print version->new($
+])'
  Unquoted string "version" may clash with future reserved word at -e 
+line 1.
  5.5.30
  zen%
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(That warning is cruft you can avoid by quoting the module name: print "version"->new($]).)

Hugo