The set command is
used to write and read variables. Tcl creates the variable with the
set command. Variables allow you to store values for use
later or in other commands. They exit only inside the script
and only for as long as the script runs. These script variables
exist only inside the script and are not available to WebAccess
displays or tags unless you use the BINDVAR or SETVAL
or GETVAL commands to pass the value of the script variable
to a WebAccess TAG (or read the value of the tag into the
variable). For example, the following command modifies the variable
x to
hold the value 73:
set x 73
You don't declare variables in Tcl: a variable is created automatically the first time it is set. Tcl variables don't have types: any variable can hold any value.
To use the value of a variable in a command, use variable substitution as in the following example:
expr $x*3
When a $ appears in a
command, Tcl treats the letters and digits following it as a
variable name, and substitutes the value of the variable in place
of the name. In this example, the actual argument received by the
expr
command will be 32*3 (assuming that
variable x was set as in the
previous example). You can use variable substitution in any word of
any command, or even multiple times within a word:
set cmd expr
set x 10
$cmd $x*$x
For example, the following set of
commands modifies the variable x2 to hold the value
of tag4 where tag4
is an IO Tag.
BINDVAR x2 tag4
Set x2 10
SETVAL tag4=10
The set x2 11 is equivalent to
SETVAL tag4=11