Ranked in these QuestionsQuestion Ranking
Pro Sane quoting rules
Unlike in *sh you don't need to quote your variable substitutions ('"$1"').
With a little care you can have the same script work on Linux, *BSD, OS X and Windows.
Pro Widely available
You can expect a reasonably recent version of Tcl to either installed or available in the repositories of any popular open source *nix.
Pro Standard library
Unlike *sh Tcl has a rich standard library.
Pro Everything is a string
Tcl can operate at the same level of abstraction as the POSIX shell, which makes it easier to manipulate the output of other programs.