Regular expression collation of Linux text processing

^ Beginning of the line.

$ end of line.

. Any character other than the line break.

* The preceding character repeats 0 to several times.

. * Used to match all characters.

[] Define a set of characters that match any one by one characters in the group (note!) Just one within the group! ）

[^] Performs an inverse operation on characters within a character group (without any one by one characters in a group)

^[] The line at the beginning of the string within the group.

^[^] A line that begins with a string that is not within a group.

[A-z] matches a lowercase letter.

[A-z] matches an uppercase letter.

[A-z] matches a lowercase and uppercase letter.

[0-9] matches a number of 0-9.

\< Match Word Header

\> match end of Word

(The definition of a word in the regular is that it is separated by a space or other special character, and successive strings are treated as words.) ）

Expansion of the Regular:

? Previous characters match 0 or 1

+ Previous characters match 1 or more

| logic or, for example abc|def ABC or DEF

() parentheses, for grouping, example: A (Bc|de) f

The meaning is ABCF or adef.

S{n} s was repeated n times.

S{n,} s repeats at least n times, even more times.

S{n,m} s repeats at least n times and repeats at most m times.

POSIX-defined character classifications:

[: Alnum:] Alphanumeric characters.

Match range is [a-za-z0-9]

[: Alpha:] Alphabetic characters.

Match range is [a-za-z]

[: Blank:] Space or tab characters.

Match range is space and TAB key

[: Cntrl:] Control characters.

Match control keys such as ^m to press CTRL + V and press ENTER to output

[:d Igit:] Numeric characters.

Match all numbers [0-9]

[: Graph:] Characters that is both printable and visible. (A space is print-

Able, but no visible, while a-a is both.)

Matching all visible characters without spaces and tabs is all the symbols you can see with your eyes on your keyboard in a text document

[: Lower:] lower-case alphabetic characters.

lowercase [A-z]

[:p rint:] Printable characters (characters that is not control characters.)

Match all visible characters including spaces and tab

All symbols that can be printed on the paper

[:p UNCT:] Punctuation characters (characters, digits, con-

Trol characters, or space characters).

Special input symbol +-=) (*&^%$#@!~ ' |\ "' {}[]:;? />.<,

Note that it does not contain spaces and tab

This set is not equal to ^[a-za-z0-9]

[: Space:] Space characters (such as space, tab, and FormFeed, to name a few).

[: Upper:] Upper-case alphabetic characters.

uppercase [A-z]

[: Xdigit:] Characters that is hexadecimal digits.

16 binary number [0-f]

How to use:

[[email protected] ~]# grep--color ' [[: Alnum:]] '/etc/passwd

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Regular expression collation of Linux text processing