AWK是否支持动态用户定义的变量？ [英] Does awk support dynamic user-defined variables?

问题描述

AWK支持这样的：

awk '{print $(NF-1);}'

而不是用户定义的变量：

but not for user-defined variables:

awk '{a=123; b="a"; print $($b);}'

顺便说一句，外壳支持这样的：

by the way, shell supports this:

a=123;
b="a";
eval echo \${$b};

我

如何才能实现我的目的AWK？

How can I achieve my purpose in awk?

推荐答案

目前不。不过，如果你提供了一个包装，这是（有点哈克和肮脏的）成为可能。
我们的想法是使用@操作符，在最新版本的gawk介绍。

Not at the moment. However, if you provide a wrapper, it is (somewhat hacky and dirty) possible. The idea is to use @ operator, introduced in the recent versions of gawk.

这@操作符通常用于按名称来调用一个函数。
所以，如果你有

This @ operator is normally used to call a function by name. So if you had

function foo(s){print "Called foo "s}
function bar(s){print "Called bar "s}
{
    var = "";
    if(today_i_feel_like_calling_foo){
        var = "foo";
    }else{
        var = "bar";
    }
    @var( "arg" ); # This calls function foo(), or function bar() with "arg"
}

现在，这是它自己的有用。
假设我们知道变种名称预先，我们可以写一个包装来间接修改，并获得瓦尔

Now, this is usefull on it's own. Assuming we know var names beforehand, we can write a wrapper to indirectly modify and obtain vars

function get(varname, this, call){call="get_"varname;return @call();}
function set(varname, arg, this, call){call="set_"varname; @call(arg);}

所以，现在，您要prrvide按名称访问的每个变量名称，要声明这两个函数

So now, for each var name you want to prrvide access by name, you declare these two functions

function get_my_var(){return my_var;}
function set_my_var(arg){my_var = arg;}

和prahaps，在BEGIN {}块地方，

And prahaps, somewhere in your BEGIN{} block,

BEGIN{ my_var = ""; }

要声明它的全局访问。
然后你可以使用

To declare it for global access. Then you can use

get("my_var");
set("my_var", "whatever");

这可以在第一次出现没有用，但也有非常良好的使用情况下，如
保持瓦尔的一个链表，通过在另一变种的阵列，并且这样保持变种的名字。
它适用于阵列过了，说实话，我用这对中嵌套和连接阵列
阵列，这样我就可以通过多种阵列走路像使用指针。

This may appear useless at first, however there are perfectly good use cases, such as keeping a linked list of vars, by holding the var's name in another var's array, and such. It works for arrays too, and to be honest, I use this for nesting and linking Arrays within Arrays, so I can walk through multiple Arrays like using pointers.

您也可以写配置参考VAR名字里面的awk这样的脚本，
实际上有一个跨preTER-内-A-间preTER的东西类型，也...

You can also write configure scripts that refer to var names inside awk this way, in effect having a interpreter-inside-a-interpreter type of things, too...

不做事的最佳途径，但是，它可以完成任务，我不担心
空指针异常，或GC和这样的： - ）

Not the best way to do things, however, it gets the job done, and I do not have to worry about null pointer exceptions, or GC and such :-)

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