自己以前写的函数（总结一下，都是学习Unix高级编成练手的）

#include <stdlib.h>
#include <stdio.h>

char* getEnvWrapper(char* key) {
    char* value = getenv(key);
    if (!value) {
        value = "not found";
    }
    return value;
}


int putEnvWrapper(char*  key, char*  value) { 
   return setenv(key, value, 1);
}


int main(int argc, char** argv){
	if(argc == 2){
		char* r = getEnvWrapper(argv[1]);
		printf("GetEnv %s = %s\n", argv[1], r);
	}else if(argc == 3 ) {
		printf("SetEnv => %s:%s\n", argv[1], argv[2]);
		int r = putEnvWrapper(argv[1], argv[2]);
		printf("GetEnv result code = %d\n", r);
	}else {
		printf("usage : ./envop key [value]\n");
	}
}