Regular expression of shell programming (grep of shell script text three swordsmen)

Catalog

1 Overview of regular expressions

1.1 Regular expression definition

1.1.1 Regular expressions make up

2 Basic regular expression metacharacters  

3 Common pipeline commands

3.1 grep

3.2 cut（ Column interceptor ）

3.3 sort

3.4 uniq

3.5 tr

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1 Overview of regular expressions

Regular expressions , Also known as regular expression .（Regular Expression）, In code it is often abbreviated as regex、regexp or RE. Regular expressions are often used for retrieval 、 Replace those that match a pattern （ The rules ） The text of .

There is more than one regular expression , and Linux Different programs in may use different regular expressions , Tools ：grep、sed、awk、egrep

1.1 Regular expression definition

Regular expressions , Also called normal expression 、 Regular expressions

Use strings to describe 、 Match a series of strings that conform to a certain rule

1.1.1 Regular expressions make up

• Ordinary character ： Case letters 、 Numbers 、 Punctuation and some other symbols
• Metacharacters ： Special characters with special meaning in regular expressions

Metacharacters are special characters with special meaning in regular expressions , It can be used to specify its leading characters （ The character before the metacharacter ） The occurrence pattern in the target object

2 Basic regular expression metacharacters  

Common metacharacters
\	Escape character ,\!、\n etc.
^	Match the beginning of the string
$	Match the end of the string
.	Matching elimination \n Any character other than
*	Match the front face expression 0 Times or times
[ ]	Match a character in the list
[^ ]	Match any character that is not in the list （ Take the opposite ）
\{n,m\}	Match the previous subexpression n To m Time , Yes \{\n}、\{n,\}、\{n,m\} Three formats
+	Match the front face expression 1 More than once
？	Match the front face expression 0 Time or 1 Time
()	Take the string in parentheses as a whole
|	Match a string of words by or

3 Common pipeline commands

3.1 grep

grep [ Options ] … Search for conditions   Target file

Common options
-E	Open extension （Extend） Regular expression of
-c	Calculate find “ Search string ” The number of times
-i	Ignore case differences , All cases are treated the same
-o	Only the string matched by the pattern
-v	Reverse selection （ Reverse lookup , Output lines that do not match the search criteria ）
-n	Sequential output line number

example 1

Method 1

Method 2

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3.2 cut（ Column interceptor ）

cut Command to cut bytes from each line of a file 、 Characters and fields and put these bytes 、 Write characters and strings to standard output

Format ：cut [ Options ] Parameters

Common options
-b	Intercept by byte
-c	Intercept by character , Commonly used in Chinese
-d	Specify what to use as the delimiter to intercept , The default is tab
-f	Usually and -d Together

example 1

Method 1

Method 2

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3.3 sort

sort It is a tool to sort the contents of files in behavioral units

Format ：sort [ Options ] Parameters

Common options
-t	Specify the separator , By default [Tab] Key or space division
-k	Specify sorting area
-n	Sort by number , The default is to sort in text
-u	Equate to uniq, Indicates that only one row of the same data is displayed .（ Be careful ： If there is a space at the end of the line, de duplication will not succeed ）
-r	Reverse sorting , The default is ascending ,-r It's in descending order
-o	Transfer the sorted results to the specified file

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3.4 uniq

uniq The command is used to check and delete the repeated rows and columns in the text file , Generally speaking, it is related to sort Command in combination with

Format ：uniq [ Options ] Parameters

Common options
-c	Count the number of repeated rows
-d	Show only duplicate lines
-u	Show only rows that appear once

example 1

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3.5 tr

Commonly used to replace characters from standard input 、 Compress and delete .

Format ：tr  [ Options ]  [ Parameters ]

Common options
-d	Delete character
-s	Delete all duplicate characters , Keep only one

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