Tcl vs Rebol

Unlike *sh Tcl has a rich standard library.

Unlike in sh you don't need to quote your variable substitutions ('"$1"').
Expanding of arguments occurs mostly explicit and if yet expected in-place (e. g. using eval or subst) it follows strict and well clear rules.
So exec test $argv would execute test with single argument.
And appending {*} before $argv would execute test with all arguments (list expansion).

With a little care you can have the same script work on Linux, *BSD, OS X and Windows.

You can expect a reasonably recent version of Tcl to either installed or available in the repositories of any popular open source *nix.

Tcl can operate at the same level of abstraction as the POSIX shell, which makes it easier to manipulate the output of other programs.

Tcl enables easy deployment through self-contained binaries known as starpacks.

Want to run something 5 times? Here you go: set i 0; time { puts done-[incr i] } 5
If you need real conditional cycle? Not a problem: for {set ready 0; set i 1} {$i <= 100 && !$ready} {incr i} { if {[exec do-some-thing] eq "ready" } {set ready 1} }
Want to measure performance of something or repeat it max 300 times and not longer than 1 seconds? Very simple: timerate { after 20 } 1000 300
How about notifying yourself when some http-server is back online? Sure thing: while {[catch { close [socket localhost 80] }]} { after 1000 }; puts "\7\7\7ONLINE!"
And you can do it also fully asynchronously using events etc.

Rebol's name came from "Relative Expression Based Object Language". Rebol is a functional language and everything is an expression that returns a value. Things that have to be baked into the grammar in other languages are simple function calls with block arguments in Rebol.

Code is data, and data can be code. Rebol is based on a simple block data structure, used both for data and for the code itself. Blocks can be manipulated programmatically, and then evaluated as code. This makes metaprogramming easy in Rebol.

Almost natural language, for example: write %out.html read http://google.com.

Beginners are usually stuck making command-line applications in other languages, because GUIs are too hard. Rebol GUIs are easy enough to start with.

Rebol's simple homoiconic syntax makes it easy to create "Rebol dialects"--domain-specific languages optimized for a particular purpose. The Rebol distribution includes many of these, and users are free to create more. These DSLs make tasks that would be complicated to express in other languages easy.