reverse a string or list

you could try something like this:

set name [DNS::question name]
set reverse "[getfield $name "." 4].[getfield $name "." 3].[getfield $name "." 2].[getfield $name "." 1]"

A method I've used to reverse order a delimited string would be like this (tested in

tclsh

set strOrig "aaa.bbb.ccc.ddd"
set listOrig [split $strOrig "."]
set listReversed [list ]
for {set i [llength $listOrig]} {[incr i -1] >= 0} {} {lappend listReversed [lindex $listOrig $i]}
set strReversed [join $listReversed "."]

or a slightly more generic approach in case you don´t have a fixed number of digits and want to use list functions:

set ip_addr [IP::client_addr]
set separator "."
for { set digit [expr {[llength  [split $ip_addr $separator]] -1 }] } { $digit >= 0 } { incr digit -1 } {
    lappend reverse_order [lindex [split $ip_addr $separator] $digit]
}
set reverse_ip [join $reverse_order $separator]

But for sure Brad´s solution is way faster. +1 🙂