019-case for while until

Case语句
    case...esac结构用来等量替换if... elif ... elif .. fi的结构。
    examples:

#!/bin/bash

arg="-f"
case $arg in
        -f)
                echo f...
                ;;            #A must here
        -d|--directory)        #allow '|' for multiple matching
                echo d...
                ;;
        *)                    #'*' means default, recommended
                echo w..$arg
                ;;
esac

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for语句
    for 接受一个列表（若缺省，则列表为参数列表"$@"），并用迭代变量逐个遍历，执行循环体语句

for i in *; do file $i; done    #单行形式
#或                                # '*' 等价于 ls
for i in *
do
     file $i
        #code of works#
done
#also
for i in `seq -w 0 100`        #等宽输出
do
    printf "%s\t" $i
done

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while-until 语句