珀尔 |正则表达式中的 pos()函数

Perl 中的pos()函数用于使用 Regex 中的 'm' 修饰符返回最后匹配的位置。
pos函数可以与 Regex 中的字符类一起使用，以返回给定字符串中所有必需的子字符串位置的列表。全局运算符“g”也可以与“m”修饰符一起使用，以在整个文本中搜索子字符串。

Syntax: pos(String) 
Parameter: String after applying Regular Expression 
Returns: the position of the matched substring 
 

示例 1：使用子字符串字符

Perl

#!/usr/bin/perl
 
# Program to print position of a substring
$String = "Geeks For Geeks";
 
print" Position of 'G' in string:\n";
 
# Regex to search for substring
# using m modifier
while($String =~ m/G/g)
{
     
    # Finding the position of substring
    # using pos() function
    $position = pos($String);
    print "$position\n";
}

输出：

Position of 'G' in string:
1
11

示例 2：使用字符类

Perl

#!/usr/bin/perl
 
# Program to print position of a substring
$String = "Geeks For Geeks";
 
print "Position of all Uppercase characters:\n";
 
# Regex to search for
# all the upper case characters
# using character class
while($String =~ m/[A-Z]/g)
{
     
    # Finding the position of substring
    # using pos() function
    $position = pos($String);
    print "$position, ";
}
 
print "\nPosition of all Lowercase characters:\n";
 
# Regex to search for
# all the lower case characters
# using character class
while($String =~ m/[a-z]/g)
{
     
    # Finding the position of substring
    # using pos() function
    $position = pos($String);
    print "$position, ";
}

输出：

Position of all Uppercase characters:
1, 7, 11, 
Position of all Lowercase characters:
2, 3, 4, 5, 8, 9, 12, 13, 14, 15,

示例 3：空格的位置

Perl

#!/usr/bin/perl
 
# Program to print position of a substring
$String = "Geeks For Geeks";
 
# Regex to search for
# all the spaces
while($String =~ m/\s/g)
{
     
    # Finding the position of substring
    # using pos() function
    $position = pos($String);
    print "$position\n";
}

输出：

6
10

使用 \G 断言从指定位置进行匹配：
Perl Regex 中的\G断言用于匹配从 pos()函数指定的位置开始的子字符串，直到匹配正则表达式中指定的字符。这将返回由 'm' 修饰符指定的字符第一次出现的位置。
例子：

Perl

#!/usr/bin/perl
 
# Defining the default string
$_ = "Geeks World is the best";
 
# Terminating character
# using m modifier
m/o/g;
 
# Specifying the starting position
$position = pos();
 
# Using \G Assertion
m/\G(.*)/g;
 
# Printing the position
# and the remaining string
print "$position $1";

输出：

8 rld is the best

在上面的示例中，匹配子字符串的第一次出现的位置与剩余的字符串一起打印。如果需要为匹配字符的下一次出现重新计算位置，只需将 $1 中剩余的字符串存储到默认字符串中。
例子：

Perl

#!/usr/bin/perl
 
# Defining the default string
$_ = "Geeks World is the best among all";
 
# Terminating character
# using m modifier
m/o/g;
 
# Specifying the starting position
$position = pos();
 
# Using \G Assertion
m/\G(.*)/g;
 
# Printing the position
# and the remaining string
print "$position $1\n";
 
# To start counting from the matched character
# until the next possible match
$_ = $1;
m/o/g;
 
$position = pos();
 
# Using \G Assertion
m/\G(.*)/g;
 
# Printing the position
# and the remaining string
print "$position $1\n";

输出：

8 rld is the best among all
19 ng all