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正则表达式中的 Perl | pos()函数

原文:https://www . geesforgeks . org/perl-pos-function-in-正则表达式/

Perl 中的 pos() 函数用于使用 Regex 中的“m”修饰符返回最后一场比赛的位置。 pos 函数可以和 Regex 中的字符类一起使用，返回给定字符串中所有需要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，在整个文本中搜索子字符串。

语法: pos(字符串) 参数:应用正则表达式 后的字符串返回:匹配子字符串 的位置

示例 1: 使用子字符串

Perl 语言

#!/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";
}

Output: 

Position of 'G' in string:
1
11

示例 2: 使用角色类

Perl 语言

#!/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, ";
}

Output: 

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

例 3: 空间位置

Perl 语言

#!/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";
}

Output: 

6
10

使用\G 断言从指定位置匹配: \ GPerl Regex 中的断言用于匹配从 pos()函数指定的位置开始的子串，直到 Regex 中指定的匹配字符。这将返回由“m”修饰符指定的字符的第一次出现的位置。 例:

Perl 语言

#!/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";

Output: 

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开始计数位置，只需将$1 中的剩余字符串存储到默认字符串中。 例:

Perl 语言

#!/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";

Output: 

8 rld is the best among all
19 ng all
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