$ cat b.txt
123456789

$ cut -c 6-4,2,8,8,8,8 b.txt
28

$ gcut -c 6-4,2,8,8,8,8 b.txt 
gcut: invalid decreasing range
Try `gcut --help' for more information.

$ gcut --version
cut (GNU coreutils) 7.5
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by David M. Ihnat, David MacKenzie, and Jim Meyering.