The final type of substitution done by the Tcl interpreter is backslash substitution. This is used to quote characters that have special meaning to the interpreter. For example, you can specify a literal dollar sign, brace, or bracket by quoting it with a backslash. As a rule, however, if you find yourself using lots of backslashes, there is probably a simpler way to achieve the effect you are striving for. In particular, the list command described on page 61 will do quoting for you automatically. In Example 1-8 backslash is used to get a literal $:
set dollar \$foo => $foo set x $dollar => $foo
Only a single round of interpretation is done.
The second set command ...