bash case usage

In bash scripts, in addition to using if for conditional judgment, you can also use case for conditional judgment.
case can handle many conditions than if else, and the conditions are all matching strings
case format is as follows

case variable inCondition 1)Statement 1statement 2;;Condition 2)Statement 1statement 2;;*)Statement 1statement 2;;esca

Note:

1. Conditions are all strings, you can use simple bash wildcards such as |, [], etc. The * sign means match all strings
2. Double quotes are required at the end of the statement;;

Example

Example 1: Write a script to provide the following menu to the user
m|M) show memory usages; show memory information
d|D) show disk usages; show disk information
q|Q)quit exit

[[email protected] bash_test]# cat 14.sh#!/bin/bashcat << EOFm|M) show memory usages;d|D) show disk usages;q|Q) quitEOFread -p "input you choice " UserChoicecase $UserChoice inm|M)free -m;;d|D)df -h;;q|Q)exit 0;;*)echo "invalid character"esac[[email protected] bash_test]# ./14.shm|M) show memory usages;d|D) show disk usages;q|Q) quitinput you choice Mtotal used free shared buff/cache availableMem: 7812 3227 4086 82 498 4247

Note: The option can use | to represent or, for example, input m or M to view memory information

Example 2: Write a program that reads input from the terminal and determines whether the input is a number, lowercase letter, uppercase letter, or special character

[[email protected] bash_test]# cat CheckInput.sh#!/bin/bashread -p "input a character:" Charcase $Char in[0-9])echo "a digit";;[A-Z])echo "a upper";;[a-z])echo "a lower";;[[:punct:]])echo "A punction.";;*)echo "Special char";;esac[[email protected] bash_test]# ./CheckInput.shinput a character:Aa upper

Note: [a-z] needs to be placed after [A-Z], because [a-z] includes [A-Z] in bash, but we can also use [[:lower:]] to represent lowercase letters, [[:upper:]]Represents capital letters