Shell 语句

一 test 测试：

测试命令 test [ ] [[ ]] (( ))
打开man test 逐一介绍每个参数

浮点计算：echo 'scale=2;1/3'|bc -l
 

测试操作
命令执行后会返回到一个系统变量中 $?
如果$?值为0 表示命令执行成功 否则为失败

二流程控制： if   while   for

#!/bin/bash
read -p 'please input username:' usr
read -p 'please input passwd:' passwd

if [ $usr = 'alex' -a $passwd = 'alex3714' ];then
   echo 'login successful'
else
   echo 'username or password is worng'
fi

!/bin/bash
age=57
while :
do

read -p 'input oldboy age:' ag

if [ $ag -eq $age ];then
    echo "bingo"
    break
elif [ $ag -gt $age ];then
    echo "the age is older"
else
    echo "the age is younger"
fi

  if [ -z $ag ];then
  continue
  fi

done

#!/bin/bash
read -p 'please input your score:' score

if [ $score -ge 90 ];then
  echo 'excellent'
elif [ $score -ge 70 -a $score -lt 90 ];then
  echo 'good'
elif [ $score -ge 60 -a $score -lt 70];then
  ehco 'not bad'
else
  echo 'bad'
fi

#!/bin/bash
read -p 'input your file:  ' file
if [ -p $file ];then
   echo "$file is block file"
elif [ -f $file ];then
   echo "$file is reuler file"
elif [ -d $file ];then
   echo "$file is directory file"
else
   echo "$file is unkown"
fi

#!/bin/bash
for ((i =1;i<=9;i++))
do
   for ((j=1;j<=i;j++))
   do
     echo -n "$i*$j=$[$i*$j] "
   done
echo
done

#!/bin/bash
usr='mona'
passwd='123'
tag=true
while $tag
do
  read -p 'please input your name: ' name
  read -p 'please input your password: ' pd
  if [ $name = $usr ] && [ $pd = $passwd ];then
  echo 'login successful'
    while $tag
    do
       read -p 'input your indirction: ' cmd
       if [ $cmd = 'quit' ];then
        tag=false
       else
           $cmd
        fi
    done
  fi
done