Question

package A;
$ENV{MOJO_USERAGENT_DEBUG} =1;
use Test::Mojo;
use utf8;

....
;
1;
package B;
BEGIN{ $ENV{MOJO_USERAGENT_DEBUG =1 } };
use Test::Mojo;
use utf8;
...
;
1;

Test::Mojo包导入Mojo::UserAgent模块：

package Test::Mojo;
...
use Mojo::UserAgent;
...
1;

为什么包A中的代码，无法打开调试。包B可以吗？

Answer 1

因为Test :: Mojo在加载变量时检查变量，所以需要在此之前设置环境。

Answer 2

#!/usr/bin/env perl
# vim:set shiftwidth=4 tabstop=4 expandtab ai smartindent fileformat=unix fileencoding=utf-8 syntax=perl:
# http://perldoc.perl.org/perlmod.html#BEGIN,-UNITCHECK,-CHECK,-INIT-and-END
package init;
            { print "10. Ordinary code runs at runtime.\n"; }
END         { print "16. So this is the end of the tale.\n" }
INIT        { print " 7. INIT blocks run FIFO just before runtime.\n" }
UNITCHECK   { print " 4. And therefore before any CHECK blocks.\n" }
CHECK       { print " 6. So this is the sixth line.\n" }
            { print "11. It runs in order, of course.\n"; }
BEGIN       { print " 1. BEGIN blocks run FIFO during compilation.\n" }
END         { print "15. Read perlmod for the rest of the story.\n" }
CHECK       { print " 5. CHECK blocks run LIFO after all compilation.\n" }
INIT        { print " 8. Run this again, using Perl's -c switch.\n" }
            { print "12. This is anti-obfuscated code.\n"; }
END         { print "14. END blocks run LIFO at quitting time.\n" }
BEGIN       { print " 2. So this line comes out second.\n" }
UNITCHECK   { print " 3. UNITCHECK blocks run LIFO after each file is compiled.\n" }
INIT        { print " 9. You'll see the difference right away.\n" }
            { print "13. It merely _looks_ like it should be confusing.\n"; }
sub import {
    print "IMPORT\n";
}
1;

这应该很清楚; - ）。

换句话说：BEGIN块和“use”语句正在同一个编译步骤中按照它们出现的顺序进行评估。 BEGIN和“use”在两个例子中互换，因此在A中，BEGIN块在“use Test :: Mojo”之后执行。我的猜测是Test :: Mojo在编译时评估env var。如果它会在运行时评估它，它应该可以工作。

更多细节？ see here

Perl环境设置没有效果

2 个答案: