How the shell intercepts strings

Summary of Shell interception string methods in Linux

How does [Linux] calculate string lengths in shell scripts?

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

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} The above 4 alternatives can be used for default values. ${#parameter} This can get the length of the string. ${parameter%word} minimum intercept from the back Word${parameter%%word} to maximize the interception from the back Word${parameter#word} minimal interception from the front word${parameter# #word} The best way to intercept word above 4 is 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. Use isDelete the first occurrence of the substring, which is the left character, starting from the left, preserving the right character. Usage is #*substr, for example: Str= ' http://www. your domain name. com/cut-string.html ' echo ${str#*//The result is www. your domain name. com/cut-string.html, which deletes all characters from the left to the first "//" and its left
2. Use 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##*/The result is cut-string.html, which deletes the last occurrence of "/" and all of its left characters 3, using the% number operator. Use isDelete the first occurrence of the substring, which is the right character, starting from the right, leaving the character on the left. Usage is%substr*, for example: Str= ' http://www. your domain name. com/cut-string.html ' echo ${str%/*The result is http://www. your domain name. com, which deletes all characters from the right to the first "/" and its right 4, using the percent sign operator. Use isDelete the last occurrence of the substring, which is the right character, starting from the right, leaving the character on the left. Usage is%%substr*, for example: Str= ' http://www. your domain name. com/cut-string.html ' echo ${str%%/*The result is http://www. your domain name. com, that is, delete from the right to the last "/" and all the characters to the right of the second is also 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 0 represents the beginning of the first character on the left and 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} of which 7 The 8th character on the left starts with the result: 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 0-6 means the 6th character starts at the right, and 10 indicates the number of characters. The result is: Cut-string3, starting from the first few characters on the right to the end, using: 0-start, for example: Str= ' http://www. your domain name. com/cut-string.html ' Echo ${str:0-4} of which 0-6 Indicates that the 6th character starts at the right, and 10 indicates the number of characters. The result is: HTML Note: (the first character on the left is denoted by 0, and the first character on the right is denoted by 0-1)

How the shell intercepts strings