bash in case of usage

We see some very practical script, due to the accumulation before the bash scripts are more discrete, not a comprehensive understanding about the record here:

The case statement usage bash

Grammar rules case statement is:

Case $ variable name in 
mode 1) 
 command sequence 
 ;; 
 mode 2) 
 command sequence 2 
 ;; 
 *) 
 default command sequence      
 ;; esac
 

Note that, case comparison is the pattern, then since it is a wildcard, then:

1. Remember Wildcard itself can not enclosed in quotation marks.
2. As for whether the variable VAR can be enclosed in double quotes.
3. Also keep in mind the difference between a wildcard (pattern) and a regular expression (regular expression) of.

4. However, the use of matching pattern square brackets denote a continuous range, such as [0-9]; using the vertical bar "|" symbol represents or. 
   The last "*)" indicates the default mode, when using the previous models were unable to match the various variables, execute the command sequence "*)" after.

Examples of the case statement: a character from the keyboard input by the user, and determines whether the character is a letter, numbers or other characters, and outputs the appropriate message.

#!/bin/bash
read -p "press some key ,then press return :" KEY
case $KEY in
[a-z]|[A-Z])
echo "It's a letter."
;;
[0-9]) 
echo "It's a digit."
;;
*)
echo "It's function keys、Spacebar or other ksys."
esac

Word in Case [pattern [| pattern] ...) List ;;] ... esac
 Case / esac Standard usage is as follows: 
 Case $ Arg in 
     pattern | the Sample) # pattern or Arg in the Sample 
     ;; 
     pattern1) # Arg pattern1 in 
     ;; 
     *) #default 
     ;; 
 esac 
 arg is a parameter that you introduced, if arg pattern consistent with the content item, then it will execute the following code pattern, while the snippet places two semicolon "; ; "do at the end. 
 It may be noted "case" and "esac" is symmetric, if not remember the words, the "case" can be reversed. 

 

case statement is a wildcard matching, if not by double quotes after the wildcard, but by text processing.

After use double quotes wildcard entry into force is no longer just treated as ordinary characters.