gistfile1.h

  path = getenv("PATH");
    if (path != NULL) {
        path = strdup(path);
        for (dir = strtok(path, ":"); dir != NULL; dir = strtok(NULL, ":")) {
            strcpy(candidate, dir);
            strcat(candidate, "/");
            strcat(candidate, argv[0]);
            if (access(candidate, X_OK) == 0) {
                printf("executable is '%s' (from PATH).\n", candidate);
                return 0;
            }
        }
        free(path);
    }