EDIT (by popular and editable requirement)
http://perldoc.perl.org/functions/open.html
In your case you will have to:
my $handle;
open ($handle,'>>','/home/shared/ftp') or die("Cant open /home/shared/ftp");
print $handle "$panel_login $panel_password $root_name $root_pass $port $panel_type";
close ($handle) or die ("Unable to close /home/shared/ftp");
Alternatively you can use autodie pragma (like @Chas Owens in the comments). Thus, no verification is required (part or die (...)).
I hope this time everything works out. If so, erases this warning.
Old obsolete way
Use print (but not one liner). Just open your file earlier and get a handle.
open (MYFILE,'>>/home/shared/ftp');
print MYFILE "$panel_login $panel_password $root_name $root_pass $port $panel_type";
close (MYFILE);
http://perl.about.com/od/perltutorials/a/readwritefiles_2.htm