Perl中的$ ENV {$ variable} [英] $ENV{$variable} in perl
问题描述
在Perl中是不是通过$ ENV {$ variable}扩展变量?
Is that anyway in Perl to expand the variable by in $ENV{$variable}?
我在外壳程序中导出了"a = T"和"T = b"，并运行了Perl脚本，其中打印了"$ ENV {$ a} \ n"，但没有打印任何内容.我想"b"可以打印，那我应该在Perl中怎么做?
I exported "a=T" and "T=b" in shell, and I run the Perl script in which print "$ENV{$a}\n", but nothing printed. I want to "b" can be printed, then how should I do in Perl?
推荐答案
您说的应该链接这些环境变量，所以
Those environment variables should be chained you say, so
$ENV{ $ENV{a} };
注意:不是$a，而是a，例如$ENV{USER}等.这使用哈希%ENV(请参见 perlvar )，它具有当前环境，因此键是环境变量的名称.
Note: not $a but a, like $ENV{USER} etc. This uses the hash %ENV (see perlvar), which has the current environment, so with keys being names of environment variables.
显然在%ENV中使用Perl变量(用于shell变量的名称† )是有趣的，而不是上面的字符串文字.在这种情况下，我们需要以某种方式将该shell变量(其名称或值)传递给Perl程序，以便将其存储在变量中.不能直接使用它.
It is apparently of interest to use a Perl variable (for the shell variable's name†) in %ENV, and not a string literal as above. In that case we need to pass that shell variable, its name or the value, to the Perl program somehow so to have it stored in a variable; can't just use it directly.
顺便说一句，将变量从shell传递到Perl的方法之一就是通过导出它，然后通过%ENV使它可用.但是，它也可以照常通过命令行传递.假设使用Perl单行代码(在shell脚本中很常见)，我们有两种方法可以通过
Incidentally, one of the ways to pass a variable from shell to Perl is precisely by exporting it, what then makes it available via %ENV. However, it can also be passed as usual, via command line. Assuming the use of a Perl one-liner (common in shell scripts), we have two options for how to pass
-
perl -we'...' "$var"作为参数，在这种情况下，它可以在@ARGV
As an argument,
perl -we'...' "$var", in which case it is available in@ARGV
通过 -s命令开关，$var设置$shv变量. --标记参数的开始.
Via the -s command switch, perl -s -we'...' -- -shv="$var", what sets up $shv variable in the one-liner, with the value $var. The -- mark the start of arguments.
有关详细信息，请参见此帖子，也许还请参见
See this post for details, and perhaps this one for another, more involved, example.
注意 注释询问如何传递变量的名称(字符串a)，而不是其值($a).对于我来说，这似乎不是最好的设计.如果出于某种原因需要传递变量名称，则将 that 存储在变量(var="a")中并如上所述传递该变量是有意义的.
Note A comment asks how to pass variable's name (string a), not its value ($a). This doesn't seem as the best design to me; if the name of a variable for some reason need be passed around then it makes sense to store that in a variable (var="a") and pass that variable, as above.
但是，如果确实要传递名称本身的想法，则改为这样做，所以无论哪种方式
But if the idea is indeed to pass the name itself around, then do that instead, so either of
perl -we'...' "a"
perl -we'...' -s -- -shv="a"
其余部分相同，并且%ENV使用分配了输入的变量.
The rest is the same and %ENV uses the variable that got assigned the input.
如果使用了完整的Perl脚本(而不是单行)，则使用 Getopt ::很长，可以很好地处理广告.
If a full Perl script is used (not a one-liner) then use Getopt::Long to nicely handle arugments.
† 注释询问有关将shell变量的 name 传递给Perl变量的信息—因此，OP中的a而不是其值$a.我不确定它的用途，但它当然是可能的.
† A comment asks about passing the shell variable's name to a Perl variable — so a from the OP, not its value $a. I am a little uncertain of the utility of that but it is of course possible.
然后，如何将变量从shell传递到Perl的两种方式在传递的内容上有所不同.
The two ways for how to pass a variable from shell to Perl then differ in what is passed.
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