得之我幸 失之我命

when someone abandons you，it is him that gets loss because he lost someone who truly loves him but you just lost one who doesn’t love you.

| sh

新 case 分支

bash 的多选复合命令称为 case，它的语法规则如下所示：

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case word in
    [pattern [| pattern]...) commands ;;]...
esac

举个例子

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#!/bin/bash
# case4-1: test a character
read -n 1 -p "Type a character > "
echo
case $REPLY in
    [[:upper:]])    echo "'$REPLY' is upper case." ;;
    [[:lower:]])    echo "'$REPLY' is lower case." ;;
    [[:alpha:]])    echo "'$REPLY' is alphabetic." ;;
    [[:digit:]])    echo "'$REPLY' is a digit." ;;
    [[:graph:]])    echo "'$REPLY' is a visible character." ;;
    [[:punct:]])    echo "'$REPLY' is a punctuation symbol." ;;
    [[:space:]])    echo "'$REPLY' is a whitespace character." ;;
    [[:xdigit:]])   echo "'$REPLY' is a hexadecimal digit." ;;
esac

case 命令检查一个变量值，在上述例子中，就是 REPLY 变量的变量值，然后试图去匹配其中一个具体的模式（模式以一个 “)” 为终止符），当与之相匹配的模式找到之后，就会执行与该模式相关联的命令，并且在该例子中找到一个模式之后，就不会再继续寻找

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$ ./case4-1
Type a character > a
'a' is lower case.  # 但其实 a 既是小写字母，也是一个十六进制的数字，但是上述例子在找到一个模式之后，无法再继续寻找新的模式

以前一直觉得 case 命令是只能执行某一个模式之后对应的命令（事实上早于版本号 4.0 的 bash，case 语法的确只允许执行与一个成功匹配的模式相关联的动作），而现如今则不然，现在的 bash 版本，可以添加 “;;&” 表达式来终止每个行动，并且允许 case 语句继续匹配下一条模式，而不是简单地终止运行

于是上述例子可以改成以下写法

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#!/bin/bash
# case4-2: test a character
read -n 1 -p "Type a character > "
echo
case $REPLY in
    [[:upper:]])    echo "'$REPLY' is upper case." ;;&
    [[:lower:]])    echo "'$REPLY' is lower case." ;;&
    [[:alpha:]])    echo "'$REPLY' is alphabetic." ;;&
    [[:digit:]])    echo "'$REPLY' is a digit." ;;&
    [[:graph:]])    echo "'$REPLY' is a visible character." ;;&
    [[:punct:]])    echo "'$REPLY' is a punctuation symbol." ;;&
    [[:space:]])    echo "'$REPLY' is a whitespace character." ;;&
    [[:xdigit:]])   echo "'$REPLY' is a hexadecimal digit." ;;&
esac

这时候再执行

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$ ./case4-2
Type a character > a
'a' is lower case.
'a' is alphabetic.
'a' is a visible character.
'a' is a hexadecimal digit.

be slow to promise and quick to perform.

ESC