Shell scripts--string interception

If you want to intercept a string, you can do it by manipulating the subscript or pointer in C + +, and in a shell script, there are several ways to do this if you want to specify a string for interception:

The following examples are used:str= "hi/i/am/just/a/string"

• ${str#*char} indicates that all characters to the left of the first char are deleted from the left , and the right string is truncated
  

#!/bin/bashstr=hi/i/am/just/a/stringecho ${str}cut=${str#*/}echo ${cut}

In fact * can be regarded as a wildcard character, that is, all characters to the left of Char are deleted;

To run the program:

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• ${str##*char} indicates that all characters to the left of the last char are deleted from the left , capturing the right string

Replace the example program with the following:

cut=${str##*/}

To run the program:

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• ${str%char*} indicates that all characters to the right of the first char are deleted from the right , and the left string is truncated
  

Replace the example program with the following:

cut=${str%/*}

The same * can be seen as a wildcard character, indicating that all characters on the right are deleted, leaving the left side;

To run the program:

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• ${str%char*} indicates that all characters to the right of the last char are deleted from the right , capturing the left string
  

Replace the example procedure as follows:

cut=${str%%/*}

To run the program:

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• ${str:n:m} means to intercept M characters starting from the nth character on the left , excluding the nth character

Replace the example program with the following:

Cut=${str:3:4}

Represents the next 4 characters starting from the 3rd character on the left, or 0 for the first character , but including the first character;

To run the program:

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• ${str:n} indicates that all subsequent characters are truncated from the nth character on the left , excluding the nth character
  

Change the above procedure to read as follows:

Cut=${str:7}

Represents all characters starting at the left of the 7th character, whichever follows;

To run the program:

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• ${str:0-n:m} means to intercept M characters starting from the nth character on the right , including the nth character
  

Replace the example program with the following:

Cut=${str:0-7:3}

Starts at the 7th character starting at the right, including the seventh character itself, and intercepts three characters;

To run the program:

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• ${str:0-n} represents all characters following the beginning of the nth character on the right , including the nth character
  

Replace the example program with the following:

CUT=${STR:0-7}

Represents the beginning of the 7th character from the right to intercept all subsequent characters;

To run the program:

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• $ {STR} | cut-c n indicates the nth character to be taken from the left-hand number

Example code:

#!/bin/bashstr=hi/i/am/just/a/stringecho ${str}echo ${str} | Cut-c 7

Represents the interception of the 7th character from the left;

To run the program:

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• $ {STR} | cut-c n = intercepts all characters from the beginning of the nth character in the left-hand number, including nth
  

Change the program as above:

Echo ${str} | Cut-c 7-

Represents all the remaining characters starting from the Intercept from the 7th character on the left;

To run the program:

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• $ {STR} | cut-c n-m represents the interception of all characters from the nth character to the first m character, including the nth character, but excluding the first m characters from the left
  

Change the procedure to read as follows:

Echo ${str} | Cut-c 2-7

Represents the interception of all characters from the left 2nd character to the 7th character, including the 2nd character, excluding the 7th character;

To run the program:

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• $ {STR} | cut-c -n means to intercept all characters going forward, including the nth character, from the beginning of the left
  

Change the procedure to read as follows:

Echo ${str} | Cut-c-7

Represents the first number of characters from the left of the 7th character to delete all characters, and the preceding characters are truncated;

Run the program as follows:

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• expr substr "${str}" N M indicates that m characters are truncated from the nth character on the left
  

Sample program:

#!/bin/bashstr=hi/i/am/just/a/stringecho ${str}cut=$ (Expr substr "${str}" 3 5) Echo ${cut}

Because expr is a command, the above $ () is the command substitution, which means that the intercept starts from the 3rd character on the left and intercepts 5 characters;

To run the program:

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Finish

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Shell scripts--string interception