string reverse , a subcommand of the built-in string command, reverses strings
Returns a string containing the characters of its input argument, string, in reverse order.
Implemented in the Changes in Tcl/Tk 8.5, as part of TIP #272[L1 ].
Workaround substitute for 8.4:
proc string'reverse str { set res {} set i [string length $str] while {$i > 0} {append res [string index $str [incr i -1]]} set res } ;# RS % string'reverse "hello, world" dlrow ,olleh
Implementation notes
This command converts its argument to the "unicode" object type so that it doesn't have to use Tcl_UtfPrev() masses of times.
[SYStems]: contains a discussion on reversing strings