Linux Regular expression syntax

Basic Components :

The basic component of a regular expression.

Regular expressions	Describe	Example
\	Escape characters, escaping special characters, ignoring their special meanings	A\.B matches a.b, but does not match AJB,. Escaped as a special meaning
^	Matches the beginning of the line, awk, ^ is the start of the matching string	^tux matches lines starting with Tux
$	Matches the end of the line, in Awk, $ is the ending of the matching string	tux$ matches lines ending with Tux
.	Matches any single character except the line break \ n, awk can	AB. Matches an ABC or bad, does not match ABCD or Abde, only matches single character
[ ]	Match any one of the characters contained in [character]	COO[KL] can match cook or cool
[^ ]	Match any character other than [^ character]	123[^45] can not match 1234 or 1235,1236, 1237 can
[ - ]	Matches any character in the specified range of [], to be written as an increment	[0-9] can match 1, 2 or 3 of any one of the numbers
?	Match previous items 1 or 0 times	Colou?r can match color or colour, and cannot match Colouur
+	Match the previous item 1 or more times	sa-6+ matches sa-6, sa-666, cannot match sa-
*	Match the previous item 0 or more times	Co*l matches cl, col, cool, coool, etc.
()	Match expression to create a substring to match	MA (tri)? Match Max or Maxtrix
N	Matches the previous item n times, n is a positive integer that can be 0	[0-9] {3} matches any three-digit number and can be extended to [0-9][0-9][0-9]
{N,}	The previous item must match at least n times	[0-9] {2,} matches any two-digit or more number of digits
{N,m}	Specifies that the preceding item matches at least N times, up to M times, n<=m	[0-9] {2,5} matches any number from a two-digit to a five-digit number
|	Alternate Match | Any one of two sides	AB (C|D) matches ABC or ABD

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:]]

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

Linux Regular expression syntax