perl基础：perl中@_,和1,$2,...及其类似变量的含义

Perl's a great language for special variables - variables that are set up without the programmer having to intervene and providing information ranging from the number of lines read from the current input file ( .)throughthecurrentprocessID( )andtheoperatingsystem( ^O). Other special variables effect how certain operations are performed ( |controllingoutputbuffering/flushing,forexample),orarefundamentalintheoperationofcertainfacilities?nomoresothan _ and @_.

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1.@_含义

1)是perl中默认的数组变量

比如说你想移除数组中的一个元素赋值给一个变 value方法1：你可以定义某个数组如@abcd??????my value=shift @abcd;

方法2：你没有定义任何数组
?????? my $value=shift @_;?? 和上例等效
?????? 这里perl会隐式的选择@_

2）是sub子函数中的默认参数列表.

例如：
sub funct($$) {
??? ($param1,$param2) = @_;
??? #Statement
}

再例如，有下面一段代码：
my?max_number?=?&max(1,2);?print?"1?and?2?,the?max?number?ismax_numbern";
sub max{
???? my ( num1, num2) = @_[0,1]; ## 取出参数列表中的元素。
???? ........此处省略求max运算
}

在子函数中直接shift; 就可以从@_的前端弹出一个元素.

shift;
等于
shift @_;

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@_ is the list of incoming parameters to a sub.?So if you write a sub,you refer to the first parameter in it as?$_[0],the second parameter as?$_[1]?and so on. And you can refer to?$#_?as the index number of the last parameter:
sub demo {
??print "Called with ",#_+1,"?paramsn";???print?"First?param?was_[0]n";

Note that the?English?module adds in the ability to refer to the special variables by other longer,but easier to remember,names such as @ARG for @_ and? PIDfor $. But use English; can have a detrimental performance effect if you're matching regular expressions against long incoming strings

2.$_含义

1) 为默认列表变量。在一个命令没有任何参数的时候，表示它从默认变量里读取。例如：print;等于print _;
2)默认模式匹配空间(pattern matching space)
s/.../.../;
等于
$_ =~ s/.../.../;

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Then any regular expression matches,?chops (and?lcs and many more) without a parameter,and even?prints assume you want to work on? .Thus:while( line = <FH>) {
??if ( line=?/Perl/)????printFHO$line;??????printuc line;
??}

Shortens to:
while (<FH>) {
??/Perl/ and
????print FHO ;
??print uc;
??}
3. 1, 2,...等含义

以数字为名的变量保存的是上一次匹配操作（/pattern/）中，第n个小括号中的原符号所匹配内容。 ??
1就是第一对小括号中的原符号所对应的匹配内容。 2就是第二对小括号中的原符号所对应的匹配内容。

内插功能： ?