Summary of usage of regular expressions in Linux

First: In Linux, the regular expression is for the content of the file. Check in the Shell's grep,sed, awk and other related commands.

Metacharacters of regular Expressions:

. : Represents any character

Number of characters anchor:

*: Indicates that * previous characters or patterns appear any time, including 0 times

？ Said Before the characters appear 0 or one time, it should be noted that in Linux needs to be \?.

\{m,n\}: Indicates that the preceding character or pattern appears at least m times, up to N times

\{m,\}: Indicates that the characters preceding it appear at least m times

\{0,n\}: Indicates that the character preceding it appears at most n times

Location anchoring:

^: denotes the beginning of the character following it

$: Indicates the end of the character in front of it

^$: Indicates a matching blank line

Match words: (you need to be aware of the meaning of words.) Root is the word, R. T is not considered a word in Linuxshell)

\<word: Represents a word that matches the beginning of Word.

Word\>: Represents a word that matches the end of Word

\<word\>: Indicates that the word matches the complete word

Range Matching:

[0-9]: Indicates a matching number

[A-Z]: Indicates a matching lowercase letter

[A-Z]: indicates matching uppercase letters

[[:p UNCT:]]: Indicates matching punctuation

[[: Space:]]: Indicates matching whitespace characters

[[: Lower:]]: Indicates a matching lowercase letter

[[: Upper:]]: Indicates matching uppercase letters

[[: Alpha:]]: Indicates matching letters, not case-sensitive letters

[[:d Igit:]]: Indicates a matching number

[[: Alnum:]]: Indicates a matching number letter

It is important to note that range matching indicates that one character in a range can be matched. Reverse matching is also supported. [^[::]]

Summary of usage of regular expressions in Linux