变量赋值

set

set varName ?value?

If value is specified, then the contents of the variable varName are set equal to value.
If varName consists only of alphanumeric characters, and no parentheses, it is a scalar variable.
If varName has the form varName(index), it is a member of an associative array.

Example

set Y 1.25   ;#变量Y赋值为1.25#打印变量Y 的值
puts $Yset str "this is a string"
puts $str

替换 Substitutions “”

使用{} 和 “” 都可以将其内部的多个参数，字符组合成一个参数。但是{}与"“存在这差异。在下面将会有介绍。
1、”"
将单词分组在双引号中，这样就可以在引号中进行替换——或者用更花哨的术语来说，就是“插值”。然后替换的组作为单个参数进行计算。因此，在puts命令中

set varName "12 dollars"
puts "The current stock value is $varName"

在上面的例子中我们可以看到，在""中的$varName作为一个变量的替换，最终输出的结果是

 The current stock value is 12 dollars

Backslashes \

通常，\禁止替换紧跟在\后面的字符。
但是下面这些作为转义字符，可以被替换为不同的特定的含义。
在文本末尾的 \ 表示忽略换行。

Example2

set Z Albany
set Z_LABEL "The capital of New York is: "puts "$Z_LABEL $Z"   ;# Prints the value of Z
puts "$Z_LABEL \$Z"  ;# Prints literal $Z instead of the value of Zputs "\nBen Franklin is on the \$100.00 bill"set a 100.00
puts "Washington is not on the $a bill"    ;# Not what you want
puts "Lincoln is not on the $$a bill"      ;# This is OK
puts "Hamilton is not on the \$a bill"     ;# Not what you want either
puts "Ben Franklin is on the \$$a bill"    ;# But, this is OKputs "This string comes out\
on a single line"

替换 Substitutions {}

前面提到了在替换中{} 与 “” 有着不同的行为。下面这里通过几个实际的例子展示{} 与 “” 在tcl解释器中的不同。
1 、在{}中无法实现变量的替换，也就是说，在{}中$varName 将无法替换为前面使用set varName lala中定义的变量的值lala,在{}中还是显示$varName
2、如果字符串已经分组了，用引号或大括号，并且大括号出现在分组的字符串的中间(即"foo{bar")，那么大括号被当作正则字符处理，没有特殊意义。
3、在文本的末尾的 \ 依旧表示不换行。

Example3

set Z Albany
set Z_LABEL "The Capitol of New York is: "puts "\n.............. examples of differences between  \" and \{"
puts "$Z_LABEL $Z"
puts {$Z_LABEL $Z}puts "\n....... examples of differences in nesting \{ and \" "
puts "$Z_LABEL {$Z}"
puts {Who said, "What this country needs is a good $0.05 cigar!"?}puts "\n.............. examples of escape strings"
puts {Note: no substitutions done within braces \n \r \x0a \f \v}
puts {But:
The escaped newline at the end of a\
string is replaced by a space}

Resulting output

.............. examples of differences between  " and {
The Capitol of New York is:  Albany
$Z_LABEL $Z....... examples of differences in nesting { and "
The Capitol of New York is:  {Albany}
Who said, "What this country needs is a good $0.05 cigar!"?.............. examples of escape strings
Note: no substitutions done within braces \n \r \x0a \f \v
But:
The escaped newline at the end of a string is replaced by a space

替换 Substitutions []

puts [readsensor [selectsensor]]

The parser scans the entire command, and sees that there is a command substitution to perform: readsensor selectsensor , which is sent to the interpreter for evaluation.
The parser once again finds a command to be evaluated and substituted, selectsensor
The fictitious selectsensor command is evaluated, and it presumably returns a sensor to read.
At this point, readsensor has a sensor to read, and the readsensor command is evaluated.
Finally, the value of readsensor is passed on back to the puts command, which prints the output to the screen.

The exceptions to this rule are as follows:

A square bracket that is escaped with a \ is considered as a literal square bracket.
A square bracket within braces is not modified during the substitution phase.

Example4

set x abc
puts "A simple substitution: $x\n"set y [set x "def"]
puts "Remember that set returns the new value of the variable:"
puts "    X: $x Y: $y\n"set z {[set x "String within quotes within braces"]}
puts "Note curly braces: $z\n"set a "[set x {String within braces within quotes}]"
puts "See how the set is executed: $a"
puts "\$x is: $x\n"set b "\[set y {This is a string within braces within quotes}]"
# Note the \ escapes the bracket, and must be doubled to be a
# literal character in double quotes
puts "Note the \\ escapes the bracket:\n \$b is: $b"
puts "\$y is: $y"