Performing variable substitution

Now that we have mapped, formatted, counted, analyzed, and generally picked our strings apart, let's look at programmatically performing variable substitution in a string. As Tcl always seems to do, we have been provided with a powerful command to simplify the task with the subst command. While you could easily invoke the set command to change the contents, subst provides the ability to alter portions of a variable by providing optional switches.

The syntax of the subst command is as follows:

subst switch string

The subst command performs variable substitution to a string. The behavior may be controlled with optional switches.

These switches are as follows:

Switch	Description
-nobackslashes	No backslash substitution will be performed.
-nocommands	No command substitution will be performed.
-novariables	No variable substitution will be performed.

How to do it…

In the following example, we will create a string that contains the value of a variable...