Shell编程基础

时间：2017/12/16 10:19:01

参考：

鸟哥的Linux私房菜：基础学习篇第四版

shell基础¶

基础语法¶

变量¶

unset 变量名：删除变量。
result=${name:-"10"}：不存在时使用默认值10。

数组

declare -a arr
arr[1]=name;
echo ${arr[1]}
# 输出数组中的所有元素
echo ${arr[@]}
# 数组长度
echo ${#arr}

参数接收¶

$0：脚本本身。
$n：第n个参数。
$#：参数个数。
$@："$1" "$2" "$3" ... 所有参数。
$*："$1 $2 $3 ..."，用空格分割。
shift n：移除前面 n 个参数，默认是1。

数值计算¶

result=$((1*2*3*4))
# 浮点运算
result=`echo "1.1*2.2*3.3"|bc`

条件语句¶

read -p "Please input your choice:[Y/N]" yn
if [ "${yn}" == "Y" -o "${yn}" == "y" ]; then
  echo "your choice is yes."
elif [ "${yn}" == "N" -o "${yn}" == "n" ]; then
  echo "your choice is no."
else
  echo "unknow choice: ${yn}"
fi
exit 0

case 语句¶

input=$1
case ${input} in
  "h")
    echo "Hello!"
    ;;
  "w")
    echo "World!"
    ;;
  *)
    echo ${input}
    ;;
esac
exit 0

for 循环¶

for in：

users=$(cat /etc/passwd | cut -d ":" -f 1)
for user in ${users}
do
  echo ${user}
done
exit 0

for do done：

for ((i=0; i<10; i++))
do
  echo ${i}
done
exit 0

while 循环¶

times=1

while [ "${times}" -ne "11" ]
do
  echo ${times}
  times=$((${times} + 1))
done

times=10
until [ "${times}" -eq "0" ]
do
  echo ${times}
  times=$((${times} - 1))
done

exit 0

函数¶

function show_message() {
  echo -n "you input is: "
}

read -p "Please enter you word:" input
show_message; echo "${input}"
read -p "Please enter you word:" input
show_message; echo "${input}"