gw1:~ # perl -nle '
>     BEGIN{
>         $input_file = shift;
>         $required_fields = shift
>     }
>     my ($field,$val) = split/:/;
>     next unless defined $field; #Skip lines with no field names
>     $fields{$field} = $val;
>     END{
>         print join ',' @fields{split/,/,$required_fields}
>     }' your_file 'email,fullName,gui'
No comma allowed after filehandle at -e line 10.