The way tcl works
from "Bryan's Practical Guide to Tcl Programming", vol 0, page 0.
The way tcl works: a line of code is parsed once. Only
once. Only ever once. Once, once, once. No exceptions at
all. None. Zero. Zip. Nada. After substitutions are performed
the first word becomes the command and all the other words
become the arguments. Always. Always, always. Always.
Always.
To avoid substitutions, place a \ before special characters,
or place a whole string of special characters inside curly
braces. Things in curly braces will never, ever, ever, ever
be parsed before being passed to the command. Never, ever,
ever. No exceptions.
The only tricky part (the _only_ tricky part) is knowing
that some commands will do their own parsing of arguments.
But only *after* the line of code is parsed in the usual
manner. Examples of these commands are "if", "expr",
"while" and a few others.
Unless you know for certain what you are doing, and know
for a fact that you want something to potentially be
evaluated twice, always, always, always provide such
arguments in curly braces. Always. Unless you know what
precisely what you are doing.
When you truly understand the above, you are a tcl expert.Reference: [L1 ]