hello guys,
i'm new to linux and in school we're learning linux commands.
like the grep, cat < file.txt, etc.

i want an application to practice with. i don't know what to look for. even if i did i'm sure someone could recommend the best application to use.

i run mac OS X on my computer, if that'll be important.

(maybe i can run linux commands on my terminal, but first i'm new to the mac itself and linux and i want something like a 'sandbox' so i don't mess anything up on my computer)

any advice will be appreciated. thanks guys.

I can come up with 2 things you could do:

1) Install a virtual machine on you mac (VMWare Fusion being one) and install a Linux distro. Now your mac is save and if you do something "unexpected", the only thing that might get broken is the distro inside the VM (which can be easily replaced).

2) OS-X is Linux alike and can be used for the basic Linux commands (use the terminal). I would suggest you create a new user and do your exercises/test as that user. Like I said: OS-X is Linux alike and not the same. Some options might not be present or work slightly different (the man pages will help you).

thank you very much. i'm installing ubuntu on my vmware now .

I would use a vmware machine like what you are doing now because, though Mac OS is similar in many respects to Linux, it is still different and might mess you up in your class. Ubuntu will do the trick, though.

ok does anyone have an idea why my install freezes when i'm installing ubuntu 12 on vmware?

I prefer VirtualBox (http://www.virtualbox.org/), and have installed many distributions without issue.

ok @goumba, i'm trying it now .
EDIT: virtualbox did the magic! thanks a lot mate!