Having an issues with my terminal. Every time I tap in a command such as `ls` i get 

```
Patricks-MacBook-Pro:~ patrickwalsh$ ls
-bash: ls: command not found

```

Running 

```
export PATH=/bin:/sbin:/usr/bin:/usr/sbin

```

fixes it but only temporarily. If I close the window and reopen for example then I am back to the above problem.

Any help or advice would be great.