_getenv.c

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

int _strlen(const char *str)
{
        int i;

        for (i = 0; str[i] != 0; i++)
                ;

        return (i);
}

char *_getenv(const char *name)
{
        extern char **environ;

        char **env;
        char *aux, *token;
        int size, size_aux;
        int i;

        size = _strlen(name);

        env = environ;

        for (; *env; ++env)
        {
                aux = *env;
                size_aux = _strlen(aux);

                token = strtok(aux, "=");
                if (token == NULL)
                        return (NULL);

                if (_strlen(token) != size)
                        continue;

                for (i = 0; i < size; i++)
                {
                        if (name[i] != aux[i])
                                break;
                        else if (name[i] == aux[i] && i == size - 1)
                                return (strtok(NULL, "="));
                }

        }


        return (NULL);
}