#!/bin/bash
echo -e "what's this\c"   
printf "\n"
echo "#-------------#"
printf "%-10s %-8s %-4s\n" name gender weight     #-10表示左对齐，10表示如果字符串不够10个字符长度，那么其他的会以空格代替。如果超过10个长度则会全部打印出来
printf "%-10s %-8s %-4.2f\n" Ada female 50.0343    #-4.2f表示浮点数打印出来一共不超过4位，还有2位小数
printf "%-10s %-8s %-4.2f\n" Albert male 51.453
printf "%-10s %-8s %-4.2f\n" Amy female 53.5423
printf "%-10s %-8s %-4.2f\n" David male 52.871

echo "#------------#"
printf "%s\n" abcdef    #printf比echo的打印功能稍微强大一些，\n是换行
printf "%s\n" abc def   #format-string被重用，abc和def都可以被打印出来
printf %s 00ooOO        #即使对于format-string不加双引号，也会正常输出
printf "please input the username:"
read username           #读入从键盘输入的字符串
printf "the username is %s\n" $username

a=4
b=8
while [ $a -lt $b ]       #while循环的格式，后面可以带中括号条件
do
  a=`expr $a + 1`
  echo "\$a=$a"
done
echo "\$a=$a"

i=100
sum=0
while (($i>=0))          #while循环的格式，后面可以带(())的格式
do
  sum=`expr $sum + $i`
  i=`expr $i - 1`
done
echo "the sum is $sum"

#while true
i=100
sum=0
until (($i<0))             #until循环和while循环是相反的。until是一旦检测到条件不成立，就退出循环
do
  sum=`expr $sum + $i`
  i=`expr $i - 1`
done
echo "the sum is $sum"

echo "please input the number 1-4"
echo "the number you input:"
read num
case $num in              #case语法规则，case 变量 in ...   esac
1) echo "you chose 1";;
2) echo "you chose 2";;
3) echo "you chose 3";;
4) echo "you chose 4";;
*) echo "you chose other numbers";;
esac

while true
do
  echo "please input 1-5:"
  read num
  case $num in
  1|2|3|4|5) echo "you input $num";;
  *) echo "you input other numbers" 
  break;; 
  esac
done