$ perl -V
Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.9-67.elsmp, archname=x86_64-linux
...
  %ENV:
    PERLDOC="-i"
  @INC:
...
$
$ echo $PERLFOO
PERLFOO: Undefined variable.
$ setenv PERLFOO bar
$ echo $PERLFOO
bar
$ perl -V
...
  %ENV:
    PERLDOC="-i"
    PERLFOO="bar"
  @INC:
...
$