Shell ———— Regular expression Basics and sed

What is a regular

　　A regular is a way to describe a character or string by combining symbols with special meanings, called regular expressions. Or, the regular is the rule used to describe a class of things.

In Linux, wildcard characters are interpreted by the shell, and regular expressions are interpreted by commands, so let's introduce three types of text processing Tools/commands: grep, sed, awk, all of which can be interpreted as regular.

Two grep

Parameters

-N: Show line numbers
-O: Show only matching content
-Q: Silent mode, no output, you have to use $? To determine the success of the execution, that is, there is no filtering to the desired content

-L: If the match succeeds, only the file name is printed, the failure is not printed, usually-rl together, grep-rl ' root '/etc
-A: If the match is successful, the matching row and the subsequent n rows are printed together
-B: If the match succeeds, the matching row and its first n rows are printed together
-C: If the match succeeds, the matching row and its n rows are printed together
--color
-C: If the match succeeds, the number of rows to match is printed
-e: Equals Egrep, extended
-I: Ignore case

-V: Inverse, mismatch
-W: Match word

Example one:

[[email protected] ~]# cat a.txt root123root asdfroot_123rootssroot 123[[email protected] ~]# grep-i "root" a.txt root123 Root asdfroot_123rootssroot 123[[email protected] ~]# grep-w "root" a.txt root 123

grep type
Grep
Fgrep
Pgrep
Egrep

The regular introduction

^ Beginning of the line
$ End of line
. Any single character other than the line break
* 0 or more of the leading characters
. * All Characters
[] Any character within a group of characters
[^] reverse each character within a character group (does not match each character in a group of characters)
^[^] lines that begin with characters within a non-character group
[A-z] lowercase letter
[A-z] capital letters
[A-z] lowercase and uppercase letters
[0-9] Number
\< words are usually separated by spaces or special characters, and successive strings are treated as words.
\> Word Tail

Extended regular sed plus-r parameter or escape
grep plus-e or egrep or escape
AWK direct support without {N,M}
can use--posix support
[[email protected] ~]#&nbs P; awk '/ro{1,3}/{print} '/etc/passwd
[[email protected] ~]#  awk--posix '/ro{1,3}/{print} ' /etc/passwd

sed-n '/roo\?/p '/etc/passwd 
Sed-rn '/roo?/p '/etc/passwd
? Leading character 0 or one
+ leading character one or more
Abc|def ABC or def
A (bc|de) f ABCF or Adef
x\{m\} x appears m times
x\{m,\} X appears m times to multiple times (at least m times)
X\{m,n\} X appears m times to N times

POSIX-defined character classification

[: Alnum:] alphanumeric characters. The
Match range is [a-za-z0-9]
[: Alpha:] alphabetic characters.
The match range is [a-za-z]
[: blank:] Space or tab characters.
The match range is a space and the 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 the print-
able, but not visible, while an A is both.)
Match all visible characters without spaces and tab 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
to all symbols printed on the paper
[:p UNCT:] punctuation characters (characters that is not letter, digits, con-< Br>trol characters, or space characters).
Special input symbol +-=) (*&^%$#@!~ ' |\ "' {}[]:;? />.<,
Note that it does not contain spaces and tab
This collection does not equal ^[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]

Three SED

Sed
Stream editor Stream editer, which is a handler for the behavior unit

Sed Stream Editor Stream editer

Grammar
sed [options] ' command ' in_file[s]
Options section
-N
-E
-I.
-F
Command section
' [Address 1, Address 2] [function] [parameter (tag)] '

method of addressing 1. Number 2. Regular
Digital
Decimal number
1 single row
1,3 range from first row to third row
2,+4 matches rows after several rows
4,~3 from line fourth to multiples of next 3
Three rows per interval from the second line
$ tail Line
1! Except the first line
Regular
The regular must be wrapped up in//
Extended regular requires the-R parameter or escape

Digital addressing: sed-n ' 1p '/etc/passwd

Regular addressing: Sed-n '/^root/p '/etc/passwd

The regular introduction

^ Beginning of the line
$ End of line
. Any single character other than the line break
* 0 or more of the leading characters
. * All Characters
[] Any character within a group of characters
[^] reverse each character within a character group (does not match each character in a group of characters)
^[^] lines that begin with characters within a non-character group
[A-z] lowercase letter
[A-z] capital letters
[A-z] lowercase and uppercase letters
[0-9] Number
\< words are usually separated by spaces or special characters, and successive strings are treated as words.
\> Word Tail

Extended regular plus-r parameter or escape
Sed-n '/roo\?/p '/etc/passwd
Sed-rn '/roo?/p '/etc/passwd
? A leading character 0 or one
+ Leading character one or more
ABC|DEF ABC or DEF
A (Bc|de) f ABCF or Adef
x\{m\} X appears m times
x\{m,\} X appears m times to multiple times (at least m times)
x\{m,n\} X appears m times to N times

Function
Delete and change
A rear plug
C Replace
I front insert
D Delete
Input/Output
P Print matching line general and-n parameter to mask default output
R read in from file
W Write to File
Control flow
! Command Counter example: 1!d Delete rows other than the first row
{} command combination commands are separated by semicolons {1h; G} can be understood as an alternative to the-e parameter

= Print line number (enter the number of the line, not the number of times the line is processed) For example: Sed-n ' 2{=;p} ' infile
N read into the next line to the pattern space example: ' 4{n;d} ' deletes line 5th
N instead, append the next line to the pattern space, and then apply the following command to the current row and the next row

Replace
s string Substitution s/old/new/

$ Sed-n ' s/root/abcdef/p '/etc/passwd

Abcdef:x:0:0:root:/root:/bin/bash

Operator:x:11:0:operator:/abcdef:/sbin/nologin

$ Sed-n ' S/ROOT/ABCDEF/GP '/etc/passwd

Abcdef:x:0:0:abcdef:/abcdef:/bin/bash

Operator:x:11:0:operator:/abcdef:/sbin/nologin

$ Sed-n ' s/root/abcdef/2p '/etc/passwd

Root:x:0:0:abcdef:/root:/bin/bash

$ Sed-n ' s/root/abcdef/3p '/etc/passwd

Root:x:0:0:root:/abcdef:/bin/bash

$ Sed-n ' S/ROOT/ABCDEF/GP '/etc/passwd

Abcdef:x:0:0:abcdef:/abcdef:/bin/bash

Operator:x:11:0:operator:/abcdef:/sbin/nologin

$

\ (\) Save matched characters for reverse reference \ n use up to 9 label label order from left to right
& Replace, use when no label is defined (reverse reference)

Shell ———— Regular expression Basics and sed