Shell script explanation (II) -- conditional test, if statement and case branch statement

One 、 Conditions for testing

1、test command （ Special testing tools ）

You can test specific conditions , And judge whether the condition is true according to the return value （ The return value is 0 Indicates that the condition is true ）

 2、 File test

File testing refers to testing based on a given path name , Determine whether the corresponding file or directory , Or judge whether the file is readable 、 Can write 、 Executable, etc .

Common operators	explain
-d	Test whether it's a directory （Directory）
-e	Test whether the directory or file exists （Exist）
-f	Whether the test is a file （File）
-r	Test whether the current user has permission to read （Read）
-w	Test whether the current user has permission to write （Write）
-x	Test whether the current user has permission to execute （eXcute）

 

 3、 Integer comparison

Integer value comparison refers to the comparison between two given integer values , Judge the relationship between the first number and the second number .

Common operators	explain
-eq	be equal to （Equal）
-ne	It's not equal to （Not Equal）
-lt	Less than （Leser Than）
-gt	Greater than （Greater Than）
-le	Less than or equal to （Lesser or Equal）
-ge	Greater than or equal to （Greater or Equal）

 4、 String comparison

String comparisons are often used to check user input 、 Whether the system environment meets the conditions , In the shell Script , It can also be used to judge whether the unknown parameters entered by the user meet the requirements .

Common operators	explain
=	String content is the same
!=	String content is different ,！ The sign means the opposite
-z	The string content is empty
-n	Check if there is a string

 LANG Environment variables represent languages and character sets  

PWD Indicates the current working directory

HOME Represents the user's Host Directory

 5、 Logic test

Determine the dependency between two or more conditions

Common operators	explain
-a or &&	Logic and , And it means
-o or ▕▕	Logic or , Or it means
！	Logical not

 

 

  Two 、if Conditional statements

1、 Single branch

 

 

 2、 Double branch

 

 3、 Multiple branches

 

 

 4、 Example

①、 Example 1

•   Check the... In the user's home directory test.sh Does the file exist , And check whether there is execution permission

②、 Example 2 

  Prompt the user for input 100 The number of seconds in the meter race , The number of seconds required is greater than the judgment 0 And less than or equal to 10 Seconds into the trials , Greater than 10 Seconds are eliminated , If you enter other characters, you will be prompted to re-enter ; The members who enter the trial will further judge the gender of men and women , Boys in the boys group , Girls in the girls group , If the input is wrong, please prompt the error .

 

③、 Example 3

•   Prompt the user to enter content , Use if Statement to determine whether the input content is an integer , And determine whether it is even or odd

 

  3、 ... and 、case sentence

1、 structure

case  A variable's value  in 
 Model a )
    Command sequence 
;;
 Model 2 )
    Command sequence  
;;
*)
    Default command sequence 
esac

2、 Example ：

①、 Example 1

•   Prompt the user for input 100 The number of seconds in the meter race , The number of seconds required is greater than the judgment 0 And less than or equal to 10 Seconds into the trials , Greater than 10 Seconds are eliminated , If you enter other characters, you will be prompted to re-enter ; The members who enter the trial will further judge the gender of men and women , Boys in the boys group , Girls in the girls group , If the input is wrong, please prompt the error

②、 Example 2

•   use case The statement is decompressed according to the suffix name .tar.gz or .tar.bz2 To /opt Catalog

 

Catalog

One 、 Conditions for testing

1、test command

 2、 File test

 3、 Integer comparison

 4、 String comparison

  Two 、if Conditional statements

1、 Single branch

 2、 Double branch

 3、 Multiple branches

 4、 Example

①、 Example 1

③、 Example 3

  3、 ... and 、case sentence

1、 structure

2、 Example ：

①、 Example 1

②、 Example 2

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