Perl split函数

Perl split函数

PHP有explode函数，Python, Ruby and JavaScript 都有各自的分割（split）方式. 在perl中有split函数

文章来源：(https://perlmaven.com/perl-split)

• 1　Syntax of split

  split REGEX, STRING 按照正则表达式（regex）分割字符串
  split REGEX, STRING, LIMIT 可以最多分割成LIMIT个块
  split REGEX 如果没给字符串，默认是$_
  split 没有任何参数，$_用/\s+/作为正则表达式

• 2　Simple cases

  split 返回一个字符串列表：

use Data::Dumper qw(Dumper);

my $str = "ab cd ef gh ij";
my @words = split / /, $str;
print Dumper \@words;

result：

$VAR1 = [
          'ab',
          'cd',
          'ef',
          'gh',
          'ij'
        ];

• ３　Limit the number of parts

  当limit = 2 时，split返回两个参数

use Data::Dumper qw(Dumper);
　　
my $str = "ab cd ef gh ij";
my @words = split / /, $str, 2;
print Dumper \@words;

result：

$VAR1 = [
          'ab',
          'cd ef gh ij'
        ];

• 4　Assign to scalars

  我们可以将结果分配给一个标量变量列表，而不是将结果分配给单个数组

方法一

my $str = "root:*:0:0:System Administrator:/var/root:/bin/sh";
my ($username, $password, $uid, $gid, $real_name, $home, $shell) = split /:/, $str;
print "$username\n";
print "$real_name\n";

result:
root
System Administrator

方法二

my $str = "root:*:0:0:System Administrator:/var/root:/bin/sh";
my @fields = split /:/, $str;
my $username = $fields[0];
my $real_name = $fields[4];
print "$username\n";
print "$real_name\n";

result:
root
System Administrator

方法三 使用数组切片

my $str = "root:*:0:0:System Administrator:/var/root:/bin/sh";
my @fields = split /:/, $str;
my ($username, $real_name) = @fields[0, 4];
#等价于 my ($username, $real_name) = (split /:/, $str)[0, 4];
print "$username\n";
print "$real_name\n";

result:
root
System Administrator

• 5　Split on more complex regex

  用更复杂的正则分割

use Data::Dumper;
my $str="fname    = Foolname =    Baremail=foo@bar.com";
my @array=split/=/,$str;
print Dumper(\@array);

result:
$VAR1 = [
          'fname    ',
          ' Foolname ',
          '    Baremail',
          'foo.com'
        ];

上面的结果有什么不妥的地方呢？我们发现分成的四部分中有空格的存在，而空格未必是我们想要的。 所以我们要对程序进行改进

use Data::Dumper;
my $str="fname    = Foolname =    Baremail=foo@bar.com";
my @array=split/\s*=\s*/,$str;
print Dumper(\@array);

result:
$VAR1 = [
          'fname',
          'Foolname',
          'Baremail',
          'foo.com'
        ];

• 6　Split on multiple characters 多种字符分割

  我们有这么一个字符串”[email protected]”我们既想用“=”分割，也想 用“&”分割。怎么做到呢？

use Data::Dumper;
my $str='[email protected]';
#注意这里是单引，若是双引号 [email protected]打印出来就是foo.com  下面同理
my @array=split/[=&]/,$str;
print Dumper(\@array);


result:
$VAR1 = [
          'fname',
          'Foo',
          'lname',
          'Bar',
          'email',
          '[email protected]'
        ];;

当然，如果我们知道这些是键-值对，那么我们可能希望将结果分配给哈希而不是数组

use Data::Dumper;
my $str='[email protected]';
my %array=split /[=&]/,$str;
print Dumper(\%array);


$VAR1 = {
          'lname' => 'Bar',
          'fname' => 'Foo',
          'email' => '[email protected]'
        };

• 7　Split on empty string 空字符串分割

use Data::Dumper qw(Dumper);

my $str = "Hello World";
my @chars = split //, $str;
print Dumper \@chars;

result:
$VAR1 = [
          'H',
          'e',
          'l',
          'l',
          'o',
          ' ',
          'W',
          'o',
          'r',
          'l',
          'd'
        ];

Beware of regex special characters
A common pitfall with split, especially if you use a string as the separator (split STRING, STRING) as in split ‘;’, $line; is that even if you pass the first parameters as a string it still behaves as a regex. So for example

split '|', $line;   等价于   split /|/, $line;

and both will split the string character by character. The right way to split on a pipe | character is to escape the special regex character:

split /\|/, $line;