Summary of Shell interception string methods in Linux

Reference documents:

There are eight ways to intercept a string, mainly for the following methods

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There are a number of ways to intercept strings in the shell, ${expression} There are 9 ways to use them. ${parameter:-word}${parameter:=word}${parameter:?word}${parameter:+word}  above 4 alternatives that can be used for default values. ${#parameter} This can get the length of the string.  ${parameter%word}  minimal intercept from behind word${parameter%%word}  maximum intercept from the back word${parameter#word}  Minimal interception of word${parameter# from the front #word}  maximum from the front to intercept word above 4 is the way to intercept the string. With four usages, you don't have to use the cut command to intercept a string. The first type can be divided into four cases, described below. 1. Use the  #  operator. The purpose is to delete the first occurrence of the substring, the left character, and the right character, starting from the left. Usage is #*substr, for example: Str= ' http://www. your domain name. com/cut-string.html ' echo ${str#*//} results from www. your domain name. com/ cut-string.html, i.e. delete all characters 2 from the left to the first "//" and its left, using the  ##  operator. The purpose is to delete the last occurrence of the substring, which is the left character, from the left side, leaving the right character. Usage is ##*substr, for example: Str= ' http://www. your domain name. com/cut-string.html ' echo ${str##*/} results in cut-string.html, that is, delete the last occurrence of "/" And its left all characters 3, use the  %  operator. The purpose is to delete the first occurrence of the substring, the right character, and the left character, starting from the right. The usage is%substr*, for example: Str= ' http://www. your domain name. com/cut-string.html ' echo ${str%/*} results are/HTTP// www. your domain name. com, that is, delete all characters from the right to the first "/" and the right of the 4, using the  %%  operator. The purpose is to delete the last occurrence of the substring, which is the right character, from the right, leaving the left character. Usage is%%substr*, for example: str=' http://www. your domain name. com/cut-string.html ' echo ${str%%/*} results in http://www. your domain name. com, i.e. delete from right to last "/" And its right all characters the second kind is divided into four kinds, respectively, the following: 1, starting from the left of the first few characters and the number of characters, using: Start:len, for example: Str= ' http://www. your domain name. com/cut-string.html ' Echo  ${var:0:5} where the  0  represents the first character on the left,,5  represents the total number of characters. The result is: Http:2, starting from the first few characters on the left until the end, using: Start, for example: Str= ' http://www. your domain name. com/cut-string.html ' Echo ${var:7} where  7   represents the 8th character on the left. The result is: www. your domain name. COM/CUT-STRING.HTML3, starting with the first few characters on the right and the number of characters, usage: 0-start:len, for example: str= '/http www. your domain name. com/cut-string.html ' Echo ${str:0-15:10} where the  0-6  represents the right side of the 6th character start,10  represents the number of characters. The result is: Cut-string3, starting from the first few characters on the right to the end, usage: 0-start, for example: Str= ' http://www. your domain name. com/cut-string.html ' Echo ${str:0-4} where the  0-6  indicates the right side of the 6th character starting,10  represents the number of characters. The result is: HTML Note: (the first character on the left is denoted by  0 , the first character on the right is represented by  0-1 )

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Summary of Shell interception string methods in Linux