Linux Regular expressions

Before you know the Linux regular expressions, you need to know the difference between the wildcard wildcards regular in Linux: Wildcards are used primarily for bash environments, while the regular majority is used in the Linux Musketeers (grep, sed, awk) ... and Linux in the regular and other development environment of the regular is different, we temporarily study is only the Linux environment of the regular ...

Wildcard Basics

Wildcard characters	Describe	Example
*	Any number of characters	Find. *.sh
？	Represents any one character	Find. ?. Sh
；	Continuous different command separation	ls m1;ls m2
#	Configuration file comments	# # # #crontab # #
|	Pipe character	Find. -type f-name "*.txt" | Xargs rm-f
~	User's home directory	oldboy~
-	Last Action Directory	Su-
$	Variable symbol	$PATH
/	Root	/
>	redirect	echo "Linux" >oldboy.sh
>>	Append redirect	echo "Linux" >>oldboy.sh
<	Input	Xargs–n 2 <oldboy.txt
<<	Input redirect	Xargs–n 2 <<oldboy.txt
‘	What you see in single quotes is what you gain	echo ' Date ' ==>date
“	Double quote variable substitution	echo "Date" ==>date Num=3 echo "$num" ==>3
`	Equivalent to $ ()	LS ==>oldboy.sh echo ' ls ' ==>oldboy.sh
{]	Content sequence	Touch m{1..10} CP File{,.bak}
!	Take counter	Find. -type f! -name "*.sh"
&&	And	&&
||	Or	||

Basic composition of regular expressions

Regular expressions	Describe	Example
^	Match beginning	^ABC matches lines starting with ABC
$	Match end	def$ matches a line ending with Def
.	Any one character	A.C matches ABC, ADC, etc.
\	Escape character, restore character itself meaning	\. Represents the point itself
*	Repeat 0 or more of the previous characters	o* represents 0 o or more O
.*	Any character	The ^.* represents the beginning of any character
[ABC]	Match any one of the characters in the character set	[A-z] [A-z] [0-9] any a-z,a-z,0-9
[^ABC]	Match all characters that do not contain ^	[^ABC] does not contain all the characters of ABC
A\{n,m\} A\{n,\} A\{n\}	Match repeats N to M times a character Repeat at least n times Repeat only n times	0\{0,3\} 0 repeated 0-3 times 0\{3,\} Repeat at least 3 times 0 0\{3\} only repeats 3 times 0
()	Create a substring for matching	MA (tri)? Match Max or Maxtrix

Extended Regular expression (grep–e or egrep)

Regular expressions	Describe	Example
+	Match 1 or more (* is 0 or more)	A + matches 1 to multiple a
？	Match 0 or one (. is only one)	A? Match 0 A or 1 a
|	Filter multiple characters at the same time	Grep–e "3306|1521"/etc/services

Metacharacters

Metacharacters (meta character) is a Perl-style regular expression that is supported by only a subset of text processing tools, not all text processing tools.

Regular expressions	Describe	Example
\b	Word boundaries	\bcool\b matching cool, mismatched coolant
\b	Non-word boundary	cool\b matching coolant, not matching cool
\d	Single numeric character	B\DB match Business-to-business, mismatch BCB
\d	Single non-numeric characters	B\db matching BCB, mismatch business-to-business
\w	Single word characters (letters, numbers, and _)	\w match 1 or a, mismatch &
\w	Single non-word character	\w match &, mismatch 1 or a
\ n	Line break	\ n matches a new row
\s	Single whitespace character	X\SX matches x x, does not match xx
\s	Single non-whitespace character	X\S\X matches Xkx, does not match xx
\ r	Enter	\ r Match Carriage return
\ t	Horizontal tab	\ t matches a horizontal tab
\v	Vertical tab	\v matches a vertical tab
\f	Page break	\f Match a page break

POSIX character class

The POSIX character class is a special meta-sequence (meta sequence) of a shape such as [: ...:] that can be used to match a specific range of characters

Regular expressions	Describe	Example
[: Alnum:]	Match any one letter or number character	[[: alnum:]]+
[: Alpha:]	Match any alphabetic character (including uppercase and lowercase letters)	[[: Alpha:]] {4}
[: Blank:]	Spaces and tabs (Landscape and portrait)	[[: blank:]]*
[:d Igit:]	Match any numeric character	[[:d Igit:]]?
[: Lower:]	Match lowercase letters	[[: Lower:]] {5,}
[: Upper:]	Match uppercase letters	([[: upper:]]+)?
[:p UNCT:]	Match punctuation	[[:p UNCT:]]
[: Space:]	Matches all whitespace characters including line feed, carriage return, and so on	[[: space:]]+
[: Graph:]	Matches any character that can be seen and can be printed	[[: Graph:]]
[: Xdigit:]	Any one hexadecimal number (i.e.: 0-9,a-f,a-f)	[[: xdigit:]]+
[: Cntrl:]	Any one control character (the first 32 characters in the ASCII character set)	[[: Cntrl:]]
[:p rint:]	Any one of the characters that can be printed	[[:p rint:]]

Linux Regular expressions