/etc/profile、/etc/bashrc、~/. Bashrc differences

1> etc The system management and configuration files are stored in the directory ( The system configuration )

etc/profile:  profile Set system wide environment variables and startup sequence for all users , Read this file when the user logs in , This file is for each shell Are effective .

 /etc/bashrc： For each run bash shell Of users executing this file , When bash shell When opened , The file is read . in other words , When the user shell Yes bash when , Run this file .

  Summarized below ：

/etc/profile The scope is greater than /etc/bashrc.
 /etc/profile Load the configuration environment when all users log in ,/etc/bashrc All users are executing bash shell when , Load configuration environment .

2> ~/.bashrc（ User configuration ）

This file is stored exclusively for individuals bash shell Information about , When logging in and opening a new shell when , Execute this file , In this file, you can customize the user's exclusive personal information .

modify /etc The configuration file under the path will be applied to the whole system , It belongs to system level configuration , And modify the... Under the user directory .bashrc It's just limited to user applications , Belongs to user level settings . The two are different in the scope of application , If it needs to be modified , Modify the .bashrc, That is, there is no need to root jurisdiction , And it won't affect other users .

PATH environment variable

PATH Variables determine shell Which directories will you look for commands or programs . If the directory of the command to be executed is in $PATH in , You don't have to enter the full path of the command , Just type the command directly . Some third-party software doesn't put executable files in Linux In the standard catalog of . therefore , Add these nonstandard installation directories to $PATH It's a solution . Besides , You'll also see how to deal with general environment variables .

First , As a rule , All environment variable names are uppercase . because Linux Case sensitive , You should pay attention to this . Of course , You can define some variables yourself , Such as '$path'、'$pAtH', but shell Ignore these variables .

The second point is that variable names sometimes start with '$' start , But sometimes it's not . When you set a variable , Just use the name , And there's no need to add “$”, Such as

“PATH=/usr/bin:/usr/local/bin:/bin”

If you want to get the value of a variable , You have to put... Before the variable name '$'：
       “echo $PATH”
       The currently set PATH Variable “/usr/bin:/usr/local/bin:/bin”

Otherwise , The variable name will be treated as plain text ：
       “echo PATH”
        Show “PATH”
        Handle $PATH The third thing to note about variables is ： You can't just replace variables , Instead, add the new string to the original value . in the majority of cases , You can't use “PATH=/some /directory”, Because this will delete $PATH All the other directories in , So when you run the program on the terminal , We have to give the complete path . therefore , It can only be added ：“PATH=$PATH:/some/directory”, If you want to add /usr/local/arm/3.4.1/bin Cross compile command , Then we can do “PATH=$PATH:/usr/local/arm/3.4.1/bin”
such ,PATH Set to the current value （ With $PATH To express ）＋ New catalog .

up to now , You only set up a new one for the current terminal $PATH Variable . If you open a new terminal , function echo $PATH , The old $PATH value , You can't see the new directory you just added . Because what you defined earlier is a local environment variable （ Current terminal only ）.

To define a global variable , Make it effective in the terminal opened later , You need to output local variables (export), It can be used "export" command ：

       export PATH=$PATH:/some/directory

Now if you open a new terminal , Input echo $PATH , You can also see the new settings $PATH 了 . Please note that , command 'export' You can only change the variables in the current terminal and later running terminals . It has no effect on the running terminal .

       To permanently add a directory to $PATH , As long as "export" Add the line of to .bashrc or /etc/bashrc In file .

　　 Use command :

　　sudo gedit ~/.bashrc