sidburn@sid:~$ echo $FOO

sidburn@sid:~$ FOO="bar"
sidburn@sid:~$ echo $FOO
bar
sidburn@sid:~$ perl -wle 'print $ENV{FOO}'
Use of uninitialized value $ENV{"FOO"} in print at -e line 1.

sidburn@sid:~$ 
sidburn@sid:~$ export FOO
sidburn@sid:~$ perl -wle 'print $ENV{FOO}'
bar