珀尔 |正则表达式备忘单

正则表达式或正则表达式是Perl编程的重要组成部分。它用于搜索指定的文本模式。在这种情况下，一组字符一起形成了搜索模式。它也被称为正则表达式。当用户学习正则表达式时，可能需要快速查看他不经常使用的那些概念。因此，为了提供这种便利，创建了一个正则表达式备忘单，其中包含正则表达式中使用的不同类、字符、修饰符等。

字符类

字符类用于字符字符串。这些类让用户匹配任何用户事先不知道的字符范围。

Classes	Explanation
[abc.]	It includes only one of specified characters i.e. ‘a’, ‘b’, ‘c’, or ‘.’
[a-j]	It includes all the characters from a to j.
[a-z]	It includes all lowercase characters from a to z.
[^az]	It includes all characters except a and z.
\w	It includes all characters like [a-z, A-Z, 0-9]
\d	It matches for the digits like [0-9]
[ab][^cde]	It matches that the characters a and b should not be followed by c, d and e.
\s	It matches for [\f\t\n\r] i.e form feed, tab, newline and carriage return.
\W	Complement of \w
\D	Complement of \d
\S	Complement of \s

例子：

# Perl program to demonstrate
# character class
    
# Actual String
$str = "45char";
    
# Prints match found if 
# its found in $str
# by using \w
if ($str =~ /[\w]/)
{
    print "Match Found\n";
}
    
# Prints match not found 
# if it is not found in $str
else
{
    print "Match Not Found\n";
}

输出：

Match Found

锚点

锚点根本不匹配任何字符。相反，它们匹配字符之前、之后或之间的特定位置。

Anchors	Explanation
^	It matches at the beginning of the string.
$	It matches at the end of the string.
\b	It matches at the word boundary of the string from \w to \W.
\A	It matches at the beginning of the string.
\Z	It matches at the ending of the string or before the newline.
\z	It matches only at the end of the string.
\G	It matches at the specified position pos().
\p{….}	Unicode character class like IsLower, IsAlpha etc.
\P{….}	Complement of Unicode character class
[:class:]	POSIX Character Classes like digit, lower, ascii etc.

例子：

# Perl program to demonstrate
# use of anchors in regex
    
# Actual String
$str = "55";
    
# Prints match found if 
# its found in $str
# using Anchors / 
if ($str =~ /[[:alpha:]]/)
{
    print "Match Found\n";
}
    
# Prints match not found 
# if it is not found in $str
else
{
    print "Match Not Found\n";
}

输出：

Match Not Found

元字符

元字符用于匹配 Perl 正则表达式中的模式。所有元字符都必须转义。

Characters	Explanation
^	To check the beginning of the string.
$	To check the ending of the string.
.	Any character except newline.
*	Matches 0 or more times.
+	Matches 1 or more times.
?	Matches 0 or more times.
()	Used for grouping.
\	Use for quote or special characters.
[]	Used for set of characters.
{}	Used as repetition modifier.

量词

这些用于检查特殊字符。量词分为三种

“？”它匹配 0 或 1 次出现的字符。
'+'匹配 1 次或多次出现的字符。
'*'匹配 0 次或多次出现的字符。

Using Quantifiers	Explanation
a?	It checks if ‘a’ occurs 0 or 1 time.
a+	It checks if ‘a’ occurs 1 or more time
a*	It checks if ‘a’ occurs 0 or more time
a{2, 6}	It checks if ‘a’ occurs 2 to 6 times
a{2, }	It checks if ‘a’ occurs 2 to infinite times
a{2}	It checks if ‘a’ occurs 2 time.

例子：

# Perl program to demonstrate
# use of quantifiers in regex
    
# Actual String
$str = "color";
    
# Prints match found if 
# its found in $str
# using quantifier ?
if ($str =~ /colou?r/)
{
    print "Match Found\n";
}
    
# Prints match not found 
# if it is not found in $str
else
{
    print "Match Not Found\n";
}

输出：

Match Found

修饰符

Modifiers	Explanation
\g	It is used to replace all the occurrence of string.
\gc	It allows continued search after \g match fails.
\s	It treats string as a single line.
i	It turns off the case sensitivity.
\x	It disregard all the white spaces.
(?#text)	It is used to add comment in the code.
(?:pattern)	It is used to match pattern of the non capturing group.
(?\|pattern)	It is used to match pattern of the branch test.
(?=pattern)	It is used for positive look ahead assertion.
(?!pattern)	It is used for negative look ahead assertion.
(<=pattern)	It is used for positive look behind assertion.
(	It is used for negative look behind assertion.

空白修饰符

Modifiers	Explanation
\t	Used for inserting tab space
\r	Carriage return character
\n	Used for inserting new line.
\h	Used for inserting horizontal white space.
\v	Used for inserting vertical white space.
\L	Used for lowercase characters.
\U	Used for upper case characters.

量词——修饰语

Maximal	Minimal	Explanation
?	??	It can occur 0 or 1 time
+	+?	It can occur 1 or more times.
*	*?	It can occur 0 or more times.
{3}	{3}?	Must match exactly 3 times.
{3, }	{3, }?	Must match at least 3 times.
{3, 7}	{3, 7}?	Must match at least 3 times but not more than 7 times.

分组和捕获

在正则表达式内部，这些组由“\1”引用，而在正则表达式外部，这些组由“$1”引用。这些组可以通过列表上下文中的变量赋值来获取，称为捕获。分组构造(...)创建称为捕获缓冲区的捕获组。

(…)	These are used for grouping and capturing.
\1, \2, \3	During regex matching, these are used to capture buffers.
$1, $2, $3	During successful matching, these are used to capture variables.
(?:…)	These are used to group without capturing.(these neither set this $1 nor \1)