In Tcl 8.5, the expr command has a variadic min() function.
% expr min(5,1,4,2,3) 1 % expr min(5,1.1,-17.345,1e10) -17.345
Like all math functions in Tcl 8.5, it is available as a command
% namespace import ::tcl::mathfunc::min % min 5 1 4 2 3 1
All arguments to the min must be able to be interpreted as numeric. Otherwise, you get this sort of error:
% expr min("non-numeric")
expected floating-point number but got "non-numeric"