如果在eval内部发生正则表达式匹配,则与外部环境不可见的捕获相关变量($1等)的更改.这是一个bug吗？
perlop和perlre似乎没有提到任何这样的限制.
例如：
- use strict; use warnings;
- $_ = "hello";
- eval '/(.*)/';
- print "GOT: $1\n";
得到：
- Use of uninitialized value $1 in concatenation (.) or string at -e line 1.
- GOT:
更简洁的演示是：
- perl -we '$_="foo"; eval q(/(.*)/;) ; print "GOT:$1\n";'
文档证明,本地化变量在这里是
perlvar of 5.14.0：
These variables are read-only and dynamically-scoped,unless we note otherwise.
The dynamic nature of the regular expression variables means that their value is limited to the block that they are in […]
@H_403_24@请注意,这一点的文档是absent from the 5.12.4 perldoc.
问题是局部变量.我的
perldoc -f eval(5.12.4)副本有这样的说法：
- The assignment to $@ occurs before restoration of localised
- variables,which means a temporary is required if you want to
- mask some but not all errors: [...]
联机帮助页并没有对所有这些特殊的全局变量(如$1,$和amp;可能还有其他变量)做出明确的声明,但阻止本地化和后续恢复是在这里发生的.
将变量分配给eval内部,一旦eval块保留,原始值就会被恢复.
- use strict; use warnings;
- use Test::More;
- use constant V => 'hello';
- $_ = V;
- note '*** block eval';
- eval {
- is $_,V,'input ok';
- /(.*)/;
- is $&,'in eval'; is $1,'in eval';
- };
- is $&,'after eval'; is $1,'after eval';
- note '*** without eval';
- is $_,'input ok';
- /(.*)/;
- is $&,V; is $1,V;
- done_testing;
