【Perl】Perl语言正则表达式初识

Perl语言提供的正则表达式应用非常广，事实上很多shell命令也支持Perl正则表达式，比如grep、sed等。?

Perl 正则表达式的元字符：

.                   a single character
    s                  a whitespace character (space,tab,newline,...)
    S                  non-whitespace character
    d                  a digit (0-9)
    D                  a non-digit
    w                  a word character (a-z,A-Z,0-9,_)
    W                  a non-word character
    [aeiou]             matches a single character in the given set
    [^aeiou]            matches a single character outside the given set
    [0-9]               matches all of the digits
    [a-z]               matches all of the low-case letters
    [^0-9]              matches all of the non-digits
    [^a-z]              matches all of the non-low-case letters
    (foo|bar|baz)       matches any of the alternatives specified
    ^                   start of string
    $                   end of string

*                   zero or more of the previous thing
    +                   one or more of the previous thing
    ?                   zero or one of the previous thing
    {3}                 matches exactly 3 of the previous thing
    {3,6}               matches between 3 and 6 of the previous thing
    {3,}                matches 3 or more of the previous thing

/^d+/              string starts with one or more digits
    /^$/                nothing in the string (start and end are adjacent)
    /(ds){3}/         a three digits,each followed by a whitespace
                        character (eg "3 4 5 ")
    /(a.)+/             matches a string in which every odd-numbered letter
                        is a (eg "abacadaf")
    # This loop reads from STDIN,and prints non-blank lines:
    while (<>) {
        next if /^$/;
        print;
    }

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注：

d?匹配一个数字的字符，和?[0-9]?语法一样

d+?匹配多个数字字符串，和?[0-9]+?语法一样

D?非数字，其他同?d

D+?非数字，其他同?d+?

w?英文字母或数字的字符串，和?[a-zA-Z0-9]?语法一样

w+?和?[a-zA-Z0-9]+?语法一样

W?非英文字母或数字的字符串，和?[^a-zA-Z0-9]?语法一样

W+?和?[^a-zA-Z0-9]+?语法一样

s?空格，和?[ntrf]?语法一样

s+?和?[ntrf]+?一样

S?非空格，和?[^ntrf]?语法一样

S+?和?[^ntrf]+?语法一样

b?匹配以英文字母,数字为边界的字符串

B?匹配不以英文字母,数值为边界的字符串

(pattern)?()?这个符号会记住所找寻到的字符串，是一个很实用的语法。第一个?()?内所找到的字符串变成?$1?这个变量或是?1?变量，第二个?()?内所找到的字符串变成?$2?这个变量或是?2?变量，以此类推下去。??

/pattern/i?i?这个参数表示忽略英文大小写，也就是在匹配字符串的时候，不考虑英文的大小写问题。?

?如果要在?pattern?模式中找寻一个特殊字符，如?"*"，则要在这个字符前加上??符号，这样才会让特殊字符失效

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参考资料：

http://perldoc.perl.org/perlintro.html#Regular-expressions