linux系统中PATH环境变量的查看与设定

1.查看环境变量

（1）.查看单个环境变量

[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

（2）查看所有环境变量

[root@server3 ~]# env

（3）查看所有本地定义的环境变量

[root@server3 ~]# set

2.设置环境变量

（1）.export命令

生效方法：立即生效
有效期限：临时改变，只能在当前的终端窗口中有效，当前窗口关闭后就会恢复原有的path配置
用户局限：当前用户

[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
[root@server3 ~]# export PATH=/usr/local/nginx/bin:$PATH
[root@server3 ~]# echo $PATH
/usr/local/nginx/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

#还原：
[root@server3 ~]# exit
logout
Connection to 172.25.66.3 closed.
[root@foundation66 bin]# ssh [email protected]
[email protected]'s password: 
Last login: Sun Apr 14 10:40:18 2019 from foundation66.localdomain
[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

（2）.修改~/.bashrc文件

生效方法：1.关闭当前终端窗口，重新打开一个新终端窗口就能生效
         2.输入“source ~/.bashrc”命令，立即生效
有效期限：永久有效
用户局限：当前用户

[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
#  ~ 即为 /root
[root@server3 ~]# vim  ~/.bashrc
#################
export PATH=/usr/local/nginx/bin:$PATH

[root@server3 ~]# source ~/.bashrc
[root@server3 ~]# echo $PATH
/usr/local/nginx/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
[root@server3 ~]# exit
logout
Connection to 172.25.66.3 closed.
[root@foundation66 bin]# ssh [email protected]
[email protected]'s password: 
Last login: Sun Apr 14 10:46:22 2019 from foundation66.localdomain
[root@server3 ~]# echo $PATH
/usr/local/nginx/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

#还原：
[root@server3 ~]# vim ~/.bashrc 
################
删除： export PATH=/usr/local/nginx/bin:$PATH

[root@server3 ~]# source ~/.bashrc 
[root@server3 ~]# echo $PATH
/usr/local/nginx/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
[root@server3 ~]# exit
logout
Connection to 172.25.66.3 closed.
[root@foundation66 bin]# ssh [email protected]
[email protected]'s password: 
Last login: Sun Apr 14 10:55:54 2019 from foundation66.localdomain
[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

（3）修改.bash_profile文件

生效方法：source命令
有效期限：永久有效
用户局限：当前用户

[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
[root@server3 ~]# vim .bash_profile 
#################
添加   :/usr/local/nginx/bin

[root@server3 ~]# source .bash_profile 
[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin:/root/bin:/usr/local/nginx/bin
[root@server3 ~]# exit
logout
Connection to 172.25.66.3 closed.
[root@foundation66 bin]# ssh [email protected]
[email protected]'s password: 
Last login: Sun Apr 14 11:05:47 2019 from foundation66.localdomain
[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin:/usr/local/nginx/bin

#还原：
[root@server3 ~]# vim .bash_profile
#################
删除   :/usr/local/nginx/bin

[root@server3 ~]# source .bash_profile 
[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin:/usr/local/nginx/bin:/root/bin
[root@server3 ~]# exit
logout
Connection to 172.25.66.3 closed.
[root@foundation66 bin]# ssh [email protected]
[email protected]'s password: 
Last login: Sun Apr 14 11:22:46 2019 from foundation66.localdomain
[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

（4）修改/etc/profile文件

生效方法：source命令
有效期限：永久有效
用户局限：对所有用户

[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
[root@server3 ~]# vim /etc/profile
#################
export PATH=/usr/local/nginx/bin:$PATH

[root@server3 ~]# source /etc/profile
[root@server3 ~]# echo $PATH
/usr/local/nginx/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

#还原：
[root@server3 ~]# vim /etc/profile
#################
删除： export PATH=/usr/local/nginx/bin:$PATH

[root@server3 ~]# source /etc/profile
[root@server3 ~]# echo $PATH
/usr/local/nginx/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
[root@server3 ~]# exit
logout
Connection to 172.25.66.3 closed.
[root@foundation66 bin]# ssh [email protected]
[email protected]'s password: 
Last login: Sun Apr 14 10:59:01 2019 from foundation66.localdomain
[root@server3 ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

3.常用的环境变量

PATH        #决定了shell将到哪些目录中寻找命令或程序 
HOME        #当前用户主目录 
HISTSIZE　  #历史记录数 
LOGNAME     #当前用户的登录名 
HOSTNAME　  #指主机的名称 
SHELL       #当前用户Shell类型 
LANGUGE 　  #语言相关的环境变量，多语言可以修改此环境变量 
MAIL　      #当前用户的邮件存放目录 
PS1　       #基本提示符，对于root用户是#，对于普通用户是$