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

 1 #!/usr/bin/perl
 2 #
 3 use strict;
 4 use warnings;
 5 
 6 main(@ARGV);
 7 
 8 sub main
 9 {
10     open(FH, 'short.txt');
11     while($_=<FH>) {
12         print if $_=~/regular/;
13         print if /\//;
14         print if m/regular/;
15         print if m|//|;
16     }
17     close FH;
18 }
19 
20 sub message
21 {
22     my $m = shift or return;
23     print("$m\n");
24 }
25 
26 sub error
27 {
28     my $e = shift || 'unkown error';
29     print(STDERR "$0: $e\n");
30     exit 0;
31 }

行号12==14； 13==15；

search1.pl

 1 #!/usr/bin/perl
 2
 3 
 4 #
 5 use strict;
 6 use warnings;
 7 
 8 main(@ARGV);
 9 
10 sub main
11 {
12     open(FH, 'short.txt');
13     while(my $line=<FH>) {
14         $line =~s/regular/BOB/;
15         $line =~s/a/BOB/gi;
16         print $line ;
17     }
18     close FH;
19 }
20 
21 sub message
22 {
23     my $m = shift or return;
24     print("$m\n");
25 }
26 
27 sub error
28 {
29     my $e = shift || 'unkown error';
30     print(STDERR "$0: $e\n");
31     exit 0;
32 }

s：替换substitude；

g： global；

i：忽略大小写；

extract.pl

 1 #!/usr/bin/perl
 2 #
 3 use strict;
 4 use warnings;
 5 
 6 main(@ARGV);
 7 
 8 sub main
 9 {
10     my $time = "05:24:37";
11     $time=~/(..):(..):(..)/;
12     my $hour=$1;
13     my $min = $2;
14     my $sec = $3;
15     #my ($hour,$min,$sec) = $time =~/(..):(..):(..)/;
16     message("hour:$hour,min:$min,sec:$sec");
17 }
18 
19 sub message
20 {
21     my $m = shift or return;
22     print("$m\n");
23 }
24 
25 sub error
26 {
27     my $e = shift || 'unkown error';
28     print(STDERR "$0: $e\n");
29     exit 0;
30 }

注释的15行可以等价与11至14行；

wild.pl

 1 #!/usr/bin/perl
 2 #
 3 use strict;
 4 use warnings;
 5 
 6 main(@ARGV);
 7 
 8 sub main
 9 {
10     open(FH, 'short.txt');
11     while(<FH>) {
12         /(^....)/;#以任意字母四个组合开头
13         /(....)$/;#以任意字母四个组合结尾
14         /(a...)/;#以字母a开头的四个字母组合
15         message($1) if $1;
16     }
17     close FH;
18 }
19 
20 sub message
21 {
22     my $m = shift or return;
23     print("$m\n");
24 }
25 
26 sub error
27 {
28     my $e = shift || 'unkown error';
29     print(STDERR "$0: $e\n");
30     exit 0;
31 }

wild1.pl

 1 #!/usr/bin/perl
 2 use strict;
 3 use warnings;
 4 
 5 main(@ARGV);
 6 
 7 sub main
 8 {
 9     open(FH, 'short.txt');
10     while(<FH>) {
11         my @list=/(a...)/g;#匹配没行左右的a开头的四个字符。
12         #my @list=/(a.{9})/g;#大括号表示重复的次数
13         #my @list=/(a.*s)/g;#匹配任意多个字符，知道s结尾,贪婪匹配greed
14         #my @list=/(a.*?s)/g;#匹配到第一个s结尾；和贪婪匹配对应
15         
16         message(join(':',@list)) if @list;
17     }
18     close FH;
19 }
20 
21 sub message
22 {
23     my $m = shift or return;
24     print("$m\n");
25 }
26 
27 sub error
28 {
29     my $e = shift || 'unkown error';
30     print(STDERR "$0: $e\n");
31     exit 0;
32 }

class.pl

 1 #!/usr/bin/perl
 2 # 
 3 # 
 4 #
 5 use strict;
 6 use warnings;
 7 
 8 main(@ARGV);
 9 
10 sub main
11 {
12     open(FH, 'perlre.txt');
13     while(<FH>) {
14         #my @list = /[0-9]/g;
15         #my @list = /\d+/g;
16         #my @list = /[a-zA-Z]+/g;
17         #my @list = /([173]+)/g;
18         #my @list = /([[:digit:]]+)/g;
19         #my @list = /([[:punct:]]+)/g;
20         #my @list = /(\w+)/g;
21         my @list = /(\W+)/g;
22         message(join(':',@list)) if @list;
23     }
24     close FH;
25 }
26 
27 sub message
28 {
29     my $m = shift or return;
30     print("$m\n");
31 }
32 
33 sub error
34 {
35     my $e = shift || 'unkown error';
36     print(STDERR "$0: $e\n");
37     exit 0;
38 }

例子里面是各种匹配方式得到的不同结果。

split.pl

 1 #!/usr/bin/perl
 2 #
 3 use strict;
 4 use warnings;
 5 
 6 main(@ARGV);
 7 
 8 sub main
 9 {
10     my $time = "05:27:32";
11     my ($hour,$min,$sec)=split(/:/,$time);
12     message("hour: $hour, minute: $min,second: $sec");
13     error("this is an error message");
14 }
15 
16 sub message
17 {
18     my $m = shift or return;
19     print("$m\n");
20 }
21 
22 sub error
23 {
24     my $e = shift || 'unkown error';
25     my @me = split(m|[\\/]|, $0);#这里匹配需要输出的流。
26     print(STDERR "$me[-1]: $e\n");
27     exit 0;
28 }

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。