lgtm warning - misc. 

**Describe the bug**
reference issues #320 

posix/osfileapi.c

```
line 186:
execl(shell, "sh", "-c", Cmd, NULL); /* does not return if successful */
--
  | The value of this argument may come from call to getenv and is being passed to execl
```


**Reporter Info**
Anh Van, NASA Goddard
