8. Environment Variables 1

Objective

???? There are environment variables in windows, such as the path we are familiar with ... So, is Linux there?

?

Body

???? The operating system is really not as smart as everyone thinks, but it's stupid.

For example, we enter: LS executes immediately

?

How is the operating system executed? How does it know how to execute LS? Where is the program to be executed?

Environment variables: Simply put, tell the system where to go (folder) to find the executable program according to the command.

?

View environment variables

Echo $PATH (PATH must be capitalized)

?

First, local variables (temporary)

Can be considered a session variable (process level)

1. Assigning values

Myname=fatsnake

PS: String Connection clamp double quotes

Myname=fat

Myname= $myname "Snake"

Print

echo $ fatsnake

Delete

Unset Fatsnake

?

Second, the system environment variable--path

A variable that the system is super-dependent on. When you execute a command, it automatically goes to the folder inside the variable to find " executable program "

?

?

Iii. setting and acquiring environment variables using C language

#include <stdio.h>

#include <stdlib.h>

int main (int argc,char *argv[]) {

?

???? Set Value

???? Putenv ("myname=fatsnake123");

???? Get value

???? Char *getresult=getenv ("myname");

???? printf ("MyName is%s\n", getresult);

?

???? printf ("Path is%s\n", getenv ("path"));

???? int i;

???? if (argc = = 2) {

???????? printf ("%s\n", argv[1]);

???????? if (strcmp (argv[1], "-version") = = 0) {

???????????? printf ("Version god 1.1\n");

????????}

???????? else{

???????????? printf ("%s\n", argv[1]);

????????}

????}

????

???? return 0;

}

?

Four, the experiment

The temporary variables set on the command line are not available in the C language!

Ps: Description is the temporary variable is process level, command line and C language program is two processes.

This mechanism of the system guarantees the process security, that is, the set of temporary variables will not be modified by other programs.

?

End

8. Environment Variables 1