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");

	}

}