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Function description of shell command parser
2022-07-06 09:41:00 【StevenXander】
1. shell What is it?
shell It's just an application , We can use the keyboard 、 Serial port sends commands to it , After entering the car, it will execute these commands .
With “ls -l” Command as an example ,
① Receive keyboard data and echo
such as : We use the keyboard to shell The program sends letters l, When it is received, it will be displayed on the screen
② Parse the input string , Find program , Execution procedure :
When we use the keyboard to shell When the program sends a carriage return , It knows that character input is over
a. shell Can parse strings , These strings are divided into several parts with spaces
The first 1 Part is the program name 、 Command name ,
Other parts are parameters
b. shell Will look for the program , Where to find ? Go to PATH Find the location indicated by the environment variable .
Of course, you can also specify absolute 、 Relative paths ,shell You will go directly to these paths to find the program
c. Find the program , Will start the program , And pass in parameters
2. How to set PATH
In the PATH Add /home/book For example, catalog :
2.1 Permanent setting method 1, This works for all users :
modify /etc/environment, such as :sudo gedit /etc/environment , Then add the downlink red envelope :
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/home/xue"
Then restart the system or log in again .
2.2 Permanent setting method 2, Valid only for the current user :
modify ~/.bashrc, Add or modify... At the end of the line :
export PATH=$PATH:/home/xue
Then restart the system or log in again .
2.3 Temporary settings :
Execute the following command at the terminal , This is only valid for the current terminal :
export PATH=$PATH:/home/xue
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