In Tcl, everything may be represented as a string, although internally it may be represented as a list, integer, double, or other type, in order to make the language fast.
The assignment command in Tcl is set.
When set is called with two
arguments, as in:
set fruit Cauliflower
it places the second argument (Cauliflower) in the memory space referenced
by the first argument (fruit). Set always returns the contents of the
variable named in the first argument. Thus, when set is called with two arguments, it
places the second argument in the memory space referenced by
the first argument and then returns the second argument. In
the above example, for instance, it would return
"Cauliflower", without the quotes.
The first argument to a set
command can be either a single word, like fruit or pi , or it
can be a member of an array. Arrays will be discussed in
greater detail later, for the time being just remember that many
data can be collected under a single variable name, and an
individual datum can be accessed by its index within that array.
Indexing into an array in Tcl is handled by putting the index
within parentheses after the name of the variable.
Set can also be invoked with only
one argument. When called with just one argument, it will
return the contents of that argument.
Here's a summary of the set
command.
set varName ?value?value is specified, then the
contents of the variable varName are
set equal to value .
varName consists only of
alphanumeric characters, and no parentheses, it is a scalar
variable.
varName has the form varName(index) , it is a member of an
associative array.
If you look at the example code, you'll notice that in the set command the first argument is typed
with only its name, but in the puts
statement the argument is preceded with a $.
The dollar sign tells Tcl to use the value of the variable - in
this case X or Y.
Tcl passes data to subroutines either by name or by value. Commands that don't change the contents of a variable usually have their arguments passed by value. Commands that do change the value of the data must have the data passed by name.
set X "This is a string" set Y 1.24 puts $X puts $Y puts "..............................." set label "The value in Y is: " puts "$label $Y"