Tcl在使用`$`符号时添加花括号 [英] Tcl adds curly braces when using `$` sign

问题描述

set B {pc_0::!mx_0 pi::$mx_0}
puts $B

set A ""
foreach x $B {
    lappend A $x
}

puts $A

该程序的输出为

pc_0::!mx_0 pi::$mx_0
pc_0::!mx_0 {pi::$mx_0}

奇怪的是，tcl在第二个输出中添加了花括号.我猜是因为它使用了$符号.但是我确实需要使用它，并且我不想插入大括号.该如何解释以及如何避免使用括号?

It is strange that tcl adds curly braces in second output. I guess it is because it uses $ symbol. But I really need to use it and I don't want the braces to be inserted. How this can be explained and how to avoid the braces?

推荐答案

通常，不要将列表视为字符串.假设它们没有字符串表示形式. (字符串表示形式仅对序列化，调试有用，而对用户无效).

As a general rule, don't treat lists as strings. Pretend that they don't have a string representation. (The string representation is only useful for serialization, debugging, but not for the user).

要将文本(尤其是用户输入)转换为列表，请使用 split .
要将其转换回，请使用 join .

To convert text (especially user-input) to a list use split.
To convert it back, use join.

您想要的秀:

puts [join $A]

背景:

一个列表具有转义Tcl使用的所有元字符的副作用.当您 eval 此列表时，将不会进行进一步的替换.对于生成稍后将执行的回调/代码，这是非常重要的属性:

Background:

A list have the sideeffect of escaping all meta-characters used by Tcl so no further subsitution takes place when you eval this list. This is a very important property for generating Callbacks/code that will be later executed:

set userinput [gets stdin]
set code [list puts $userinput]
eval $code

无论用户在此处输入什么，输出始终与用户输入的相同，没有任何替代.

No matter what the user enters here, the output is always the same as the user entered, without any substitution.

如果不能逃避$，则评估将尝试替换$mx_0，这很可能会失败.

If the $ would not be escaped, then an evaluation would try to substitute $mx_0, which will most likly fail.

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