lesson 3
example ①：
set Z "zhou li "
set Z_LABEL "is a boy "
puts "
................. examples of differences between " and {"
puts "$Z_LABEL $Z"
puts {$Z_LABEL $Z}
// {}将会把括号里面的东西全部原封不动的输出
example ②：
puts "
....... examples of differences in nesting { and " "
puts "$Z_LABEL {$Z}"
puts {Who said, "What this country needs is a good $0.05 cigar!"?}
// 第二行可以看出将{$Z}化简即为$Z, 所以第二行结果自然可将$Z所对应的变量输出，而不是直接输出
//第三行是“ 和的嵌套使用： 谁在外面谁就有最终的控制权