Entry widget to run \&sub_cmd on enter key

lets say I have an Entry widget where I want to run sub_cmd when
the enter key is pressed and the value of $inputcmd would then 
be evaluated from within sub_cmd and would lead to some sort of
text displayed on my Text widget.  Would I use and Entry widget
or go about it another way. 

my($input) = $frame3->Entry(-width => 100,
                            -background  => 'white',
                            -foreground  => 'black',
                            -textvariable=> \$inputcmd)->pack;
                            

I understand I cant use: -command => sub { \&sub_cmd } 
with the Entry widget.
-++**==--++**==--++**==--++**==--++**==--++**==--++**==
This message was posted through the Stanford campus mailing list
server.  If you wish to unsubscribe from this mailing list, send the
message body of "unsubscribe ptk" to majordomo@xxxxxxxxxxxxxxxxxx