variable call echo
Variable view set
View all variables (local variables and environment variables), if you only query environment variables, use the env command
variable unset
One: User-defined variables
Two: environment variables
export declares environment variables
Syntax: export variable name = variable value
You can also set a declared local variable as an environment variable
eg: name=zhangsan
export name
env view environment variables
pstree determines the process tree
Common environment variables
PATH
The path where the system finds the command, and multiple paths are separated by colons ":"
PATH="$PATH":/root/sh #Method of superimposing environment variables
PS1 (system reserved user operating system environment variable)
Variables that define the system prompt
The default is: PS1='[\u@\h \W] ' echo PS1 to view the value of the variable
Three: position parameter variable
eg:sum.sh
#!/bin/bash
sum=$(( $1+$2 ));
echo "sum is: $sum"
Execute the command: sh sum.sh 10 22 Be careful not to forget the last two numeric parameters.
eg: canshu.sh
#!/bin/bash
for i in $*
do
echo '$* = '+$i;
done
for i in $@
do
echo '$@ = '+$i;
done
Four: Predefined variables
read receives keyboard input
Syntax: read [options] [variables]
Options:
-p "prompt information": output prompt information while waiting for read input. prompt abbr
-t seconds The number of seconds to wait for input. timeout abbreviation
-n Accepts the number of characters to wait. If this parameter is not defined, the input of this parameter will not be ended until a carriage return. nchars abbr
-s hides the entered data.
eg:
read.sh
#!/bin/bash
read -t 30 -p "please input your name " name
echo -e "\n"
echo $name
read -t 30 -s -p "please input your age" age
echo -e "\n"
echo $age
read -t 30 -n 1 -p "please input your gender[F/M]" gender
echo -e "\n"
echo $gender
数字运算
a=3
b=5
method1:d=$(($a + $b)); #注意：”=”左右两边不能有空格，
Method2:f=$[$a+$b];
method3:declare -i c=$a+$b;
method4:e=$(expr $a+$b); #注意：”=”左右两边不能有空格，”+”左右两边必须要有空格
declare
运算符优先级
变量替换
环境变量配置文件
/etc/目录下的对所有用户生效，~/目录下的对当前用户生效
source 命令
修改配置文件后强制让指定配置文件生效。
语法：source 配置文件
或者. 配置文件
环境变量配置文件读取顺序图
/etc/profile的作用
/etc/bashrc的作用
~/bash_logout 注销时需要做的操作
~/bash_history 所有敲过的历史命令
shell登录信息
