perl-可选修饰符

perl-可选修饰符

可选修饰符

这些修饰符可有可无，有时候称为开关，放在正则表达式结尾的界定符右边，并改变正则表达式的默认行为。
/i  进行大小无关的匹配
/s  匹配任意字符
/x  加入空白

实例：
1)  /i修饰符可以让你在进行模式匹配时不区分大小写。

#!/perl
use strict;

print "Would you like to play a game?";
chomp($_ = <STDIN>);
if (/YES/i){
	print "You input the string : $_";
}
#end

2)用/s来匹配任意字符，默认情况下(.)号无法匹配换行符，这对大多数单行匹配的情况是符合的，但是如果字符串中有换行符时，用/s就可以完成匹配。

#!/perl
use strict;

my ($var);
$var = "I saw Barney\ndown at the bowling alley\nwith fred\nlast night.\n";
#if ($var_sub =~ /Barney.*fred/s){
if ($var =~ /Barney.*fred/s){
	print "That matching mentions fred Barney.";
}
#end

3) 用/x加入空白
在模式里随意加入空白，使它阅读更容易：
/-? \d+\.?\d*/
/ -?  \ d+ \ .? \ d* /
加入空白后更易于阅读。

附加：
.   Match any character
\w  Match "word" character (alphanumeric plus "_")
\W  Match non-word character
\s  Match whitespace character
\S  Match non-whitespace character
\d  Match digit character
\D  Match non-digit character
\t  Match tab
\n  Match newline
\r  Match return
\f  Match formfeed
\a  Match alarm (bell, beep, etc)
\e  Match escape
\021  Match octal char ( in this case 21 octal)
\xf0  Match hex char ( in this case f0 hexidecimal)


You can follow any character, wildcard, or series of characters and/or wildcard with a repetiton. Here's where you start getting some power:
*      Match 0 or more times
+      Match 1 or more times
?      Match 1 or 0 times
{n}    Match exactly n times
{n,}   Match at least n times
{n,m}  Match at least n but not more than m times