tcl - 为什么 puts with '[' 失败了？

Question

有人可以解释为什么这总是失败吗？

set hostname ""

if {$hostname eq ""} {
   puts "Usage: host [-u username] [-p password] [-f]"
   exit 5
}

if {[string length $hostname] == 0} {
   puts "Usage: host [-u username] [-p password] [-f]"
   exit 5
}

 if {[string equal $hostname ""]} {
   puts "Usage: host [-u username] [-p password] [-f]"
   exit 5
}

我收到以下错误:

invalid command name "-u"
    while executing
"-u username"
    invoked from within
"if {$s eq ""} {puts "Usage: host [-u username] [-p password] [-f]"}"

代码似乎执行得很好，但我似乎无法将 puts 与包含大括号的字符串一起使用。

Answer 1

双引号字符串中的方括号表示求值。尝试使用反斜杠转义方括号。