Bash Shell的学习

基本语法

1.输出HELLO

echo HELLO

2.输出1~100的奇数

for((i = 1;i <= 99;i+=2))
do
   echo $i
done

for i in {1..99..2}
do
    echo $i
done

seq 1 2 99

3.输入一个名字，输出Welcome “名字”

read str
echo Welcome $str

read name
echo "Welcome $name"

echo "Welcome $(</dev/stdin)"

printf "Welcome "
cat

4.输出1~50

for((i = 1;i <= 50;i++))
do
  echo $i
done

5.输出X、Y的加减乘除

read X
read Y
echo $((X+Y))
echo $((X-Y))
echo $((X*Y))
echo $((X/Y))

read X
read Y
echo `expr $X + $Y`#变量之间注意空格
echo `expr $X - $Y`
echo `expr $X \* $Y`
echo `expr $X / $Y`

6.输出整数X与Y的关系，一个字符串

read X
read Y
if [ $X -gt $Y ]
then
echo "X is greater than Y"
elif [ $X -lt $Y ]
then
echo "X is less than Y"
else
echo "X is equal to Y"
fi

7.判断是’Y’、’y’还是’N’、’n’

read c
if [[ $c = "Y" || $c = "y" ]]#也可以去掉引号
then
echo "YES"
else
echo "NO"
fi

8.给出三边长度，判断是等边，等腰，还是不等边

read X
read Y
read Z
if [[ $X -eq $Y && $Y -eq $Z ]]
then
echo "EQUILATERAL"
elif [[ $X -eq $Y || $Y -eq $Z || $X -eq $Z ]]
then
echo "ISOSCELES"
else
echo "SCALENE"
fi

9.求一行四则运算表达式的值，精确到小数点后三位

read exp
printf "%.3f\n" `echo $exp | bc -l`

10.求一整数的平均值，精确到小数点后三位

read N
sum=0
for((i = 1;i <= $N;i++))
do
  read x
  let "sum+=$x"#也可以 sum=$((sum+x))
done
#var=`echo "scale=3;$sum/$N"|bc`
printf "%.3f" $(echo $sum/$N | bc -l)