C Environment

programming C MOC

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C can store data in an environment variable.

Get all environment variables:

#include <stdio.h>
 
extern char **environ;
 
int main() {
    int i = 0;
    while(environ[i]) {
        printf("%s\n", environ[i++]);
    }
 
    return 0;
}

getenv

The stdlib.h library can get specific environment variables:

#include <stdio.h>
#include <stdlib.h>
 
int main() {
    printf("USER: %s\n", getenv("USER"));
    printf("PATH: %s\n", getenv("PATH"));
    printf("HOME: %s\n", getenv("HOME"));
    printf("ROOT: %s\n", getenv("ROOT"));
    printf("LANGUAGE: %s\n", getenv("LANGUAGE"));
    printf("PWD: %s\n", getenv("PWD"));
    printf("SHELL: %s\n", getenv("SHELL"));
    printf("COLORTERM: %s\n", getenv("COLORTERM"));
 
    return 0;
}

putenv and setenv

putenv sets environment variables in the form of putenv("MYVAL=great").

setenv sets environment variables in the form of setenv("MYVAL", "great") and can overwrite variables

unsetenv and clearenv

clearenv() removes all environment variables.

unsetenv('MYVAL') removes specific environment variables