Shell (7) case statement

Shell（7）case sentence

Preface

In a script , We often need to interact , Execute different commands according to the results of interactive input , And that's where it comes in case sentence .

And if The difference is ,case The statement is more like a menu , You don't need to make your own judgment , According to different results preset in advance , Execute the corresponding command .

One 、read command

read Commands are the main instructions we use to interact in scripts , He can define variables according to the way of interactive input .read yes Shell Built in commands , If it doesn't work Redirect , The default is to read the data entered by the user from the keyboard ; If redirected , Then you can read data from the file .read The basic format of the command is ：

read [ Options ] [ Variable name ]    # Variable names can be multiple 

Options ：

Options	Content
-p	Display prompt message , And do not use line breaks , The tip is prompt.
-n	Read at most n Stop after characters , Stop immediately if you encounter a carriage return or line change halfway .
-N	Read at most n Stop after characters , If you encounter a carriage return or line change, it will not stop .
-r	Read as is （Raw mode）, Do not interpret backslash characters as escape characters .
-s	silent mode （Silent mode）, The entered characters will not be displayed on the screen . When entering passwords and other confirmation information , It is necessary to .
-e	When getting user input , Code conversion of function keys , The character corresponding to the function key will not be displayed directly .
-d	Use string delimiter Specify the position where the reading ends , Instead of a newline （ The data read does not include delimiter）.
-a	Assign the read data to the array array, From the subscript 0 Start .
-u	Use file descriptors fd As an input source , Instead of standard input , Similar to redirection .
-t	Set timeout , If the input is not finished after this time ,read No data is stored .

example ： Enter your name interactively , And output this variable ：

Two 、case sentence

case Statement can make the structure of the script program clearer 、 distinct , Commonly used for service startup 、 restart 、 Stopped script , Some services do not provide such control scripts , Need to use case Statement writing .

case Statement is mainly applicable to the following situations ： There are many values for a variable , You need to execute different command sequences for each value . This is the case with multi - branched if The sentences are very similar , It's just if Statements need to judge multiple different conditions , and case The statement just judges the different values of a variable .

case Grammatical structure ：

case $ Variable  in   #case  Line ending must be a word “in”
 Pattern 1)         # The first mock exam must be the right bracket “)” end .
	 Command sequence 1 
	;;         # Double a semicolon “;;” Indicates the end of the command sequence .
 Pattern 2)        # In pattern string , You can use square brackets to indicate a continuous range , Such as “[0-9]” exceed 9 The number of requires a regular expression ; You can also use the vertical bar symbol  “|” Represents or , Such as “A|B”.
	 Command sequence 2
	;;
* )            # final “*)” Represents the default mode , Among them * It's equivalent to a wildcard .
	 Command sequence 3   # There is no need to add a double semicolon after the last mode .
esac           # hold case Write backwards , End of the said case sentence 

example ： Enter a character , Determine the type of character ：

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