BASH语法简介

变量声明和赋值

• 等号左右不要有空格,
• 通过export 变成全局变量，全局变量的含义还没有搞清楚
• 空格或者换行含义是一样的
• #代表注释，但是前面要有一个空格

#!/bin/bash
#a.sh
a=666
b=hello
g_user=root
export g_user #全局变量
echo $a
echo $b
echo $g_user

把命令结果赋值给变量

#!/bin/bash
#a.sh
current_date1=$(date)
current_date2=\`date\`
current_date3={\`date\`}
echo current data is [$current_date1]
echo current data is [$current_date2]
echo current data is [$current_date3]

if条件判断

#!/bin/bash
#a.sh
if [[ $1 == 1 ]]; then
    echo "first argument is 1"
else
    echo "first argument is not 1"
fi # 调用命令： bash a.sh 1 

case分支判断

#!/bin/bash
#a.sh
case $1 in
    1) echo "the case is 1" ;;
    2) echo "the case is 2" ;;
    3) echo "the case is 3" ;;
    4) echo "the case is 4" ;;
    *) echo "no case match first argument" ;;
esac # 调用命令： bash a.sh 2 

for循环语句

#!/bin/bash
#a.sh
for (( i = 0; i < 10; i++ )); do
    echo "current value is $i"
done

for i in 1 2 3 4 5; do
    echo "current value is $i"
done

while循环

#!/bin/bash
#a.sh
i=$1

while [[ $i > 0 ]]; 
do
    echo "now i's value is $i"
    let "i=i-1"
done