Perl 学习手札之九：regular expressions

Regular expressions is a very powerful method of matching patterns in text

　　there are often called "regex" or the plural "regexes".

they are used within other languages, like Perl

commonly used for search-and-replace operations

regexes can be very simple or very complex

the regex expression language is compact, so it can look more intimidating

($hour,$min,$sec) = $time = ~/(\d\d):(\d\d):(\d\d)/;

　　while($n=~s/^(-?\d+)(\d{3})/\1,\2/){}

search.pl

#!/usr/bin/perl
#
use strict;
use warnings;

main(@ARGV);

sub main
{
    open(FH, 'short.txt');
    while($_=<FH>) {
        print if $_=~/regular/;
        print if /\//;
        print if m/regular/;
        print if m|//|;
    }
    close FH;
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print(STDERR "$0: $e\n");
    exit 0;
}

行号12==14； 13==15；

search1.pl

#!/usr/bin/perl


#
use strict;
use warnings;

main(@ARGV);

sub main
{
    open(FH, 'short.txt');
    while(my $line=<FH>) {
        $line =~s/regular/BOB/;
        $line =~s/a/BOB/gi;
        print $line ;
    }
    close FH;
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print(STDERR "$0: $e\n");
    exit 0;
}

s： 替换substitude；

g： global；

i：忽略大小写；

extract.pl

#!/usr/bin/perl
#
use strict;
use warnings;

main(@ARGV);

sub main
{
    my $time = "05:24:37";
    $time=~/(..):(..):(..)/;
    my $hour=$1;
    my $min = $2;
    my $sec = $3;
    #my ($hour,$min,$sec) = $time =~/(..):(..):(..)/;
    message("hour:$hour,min:$min,sec:$sec");
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print(STDERR "$0: $e\n");
    exit 0;
}

注释的15行可以等价与11至14行；

wild.pl

#!/usr/bin/perl
#
use strict;
use warnings;

main(@ARGV);

sub main
{
    open(FH, 'short.txt');
    while(<FH>) {
        /(^....)/;#以任意字母四个组合开头
        /(....)$/;#以任意字母四个组合结尾
        /(a...)/;#以字母a开头的四个字母组合
        message($1) if $1;
    }
    close FH;
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print(STDERR "$0: $e\n");
    exit 0;
}

wild1.pl

#!/usr/bin/perl
use strict;
use warnings;

main(@ARGV);

sub main
{
    open(FH, 'short.txt');
    while(<FH>) {
        my @list=/(a...)/g;#匹配没行左右的a开头的四个字符。
        #my @list=/(a.{9})/g;#大括号表示重复的次数
        #my @list=/(a.*s)/g;#匹配任意多个字符，知道s结尾,贪婪匹配greed
        #my @list=/(a.*?s)/g;#匹配到第一个s结尾；和贪婪匹配对应
        
        message(join(':',@list)) if @list;
    }
    close FH;
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print(STDERR "$0: $e\n");
    exit 0;
}

class.pl

#!/usr/bin/perl
# 
# 
#
use strict;
use warnings;

main(@ARGV);

sub main
{
    open(FH, 'perlre.txt');
    while(<FH>) {
        #my @list = /[0-9]/g;
        #my @list = /\d+/g;
        #my @list = /[a-zA-Z]+/g;
        #my @list = /([173]+)/g;
        #my @list = /([[:digit:]]+)/g;
        #my @list = /([[:punct:]]+)/g;
        #my @list = /(\w+)/g;
        my @list = /(\W+)/g;
        message(join(':',@list)) if @list;
    }
    close FH;
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print(STDERR "$0: $e\n");
    exit 0;
}

例子里面是各种匹配方式得到的不同结果。

split.pl

#!/usr/bin/perl
#
use strict;
use warnings;

main(@ARGV);

sub main
{
    my $time = "05:27:32";
    my ($hour,$min,$sec)=split(/:/,$time);
    message("hour: $hour, minute: $min,second: $sec");
    error("this is an error message");
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    my @me = split(m|[\\/]|, $0);#这里匹配需要输出的流。
    print(STDERR "$me[-1]: $e\n");
    exit 0;
}

这里我们的正则表达式就暂时告一段落，个人感觉写的非常不好，很多的匹配方式都没有看到。

更多可以参考：http://perltraining.com.au/上的文章。