-bash: sudo: command not found

Question

     Hello all,
I have had WAY too many problems with this laptop, and at this point in its miserable little life, I've decided to just wipe the hard drive and start fresh, not caring at all what happens to the files left on there. As previously stated in one of my earlier questions (That was, might I add, never fully answered.), this late 2008 MacBook (aluminum) has a problem where it does not boot up, and just endlessly shows the gray spinning pinwheel. Four months later, that just stops, and now when trying to boot up with my normal startup disk, it brings me right to the Recovery disk and tries to reinstall OS X. I tried, it failed 5 minutes in. So I tried to wipe the hard drive, and it says:  Disk Erase failed with the error: Couldn't unmount disk.   I looked it up and I saw that if I went into the Terminal and typed: sudo diskutil unmountDisk /dev/disk0 , it would unmount the disk. But whenever I type that, it says: -bash: sudo: command not found. I have no idea how to fix this, and I would really like to be able to use my laptop again without giving somebody my money to do it for me.
                                             Thanks,
                                                  Luke

Answer 1

Clean Install of Snow Leopard
Be sure to make a backup first because the following procedure will erase
the drive and everything on it.
     1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came
         with your computer.  Insert the disc into the optical drive and restart the computer.
         After the chime press and hold down the  "C" key.  Release the key when you see
         a small spinning gear appear below the dark gray Apple logo.
     2. After the installer loads select your language and click on the Continue
         button. When the menu bar appears select Disk Utility from the Utilities menu.
         After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive
         size.)  Click on the Partition tab in the DU main window.  Set the number of
         partitions to one (1) from the Partitions drop down menu, click on Options button
         and select GUID, click on OK, then set the format type to MacOS Extended
         (Journaled, if supported), then click on the Apply button.
     3. When the formatting has completed quit DU and return to the installer.  Proceed
         with the OS X installation and follow the directions included with the installer.
     4. When the installation has completed your computer will Restart into the Setup
         Assistant. After you finish Setup Assistant will complete the installation after which
         you will be running a fresh install of OS X.  You can now begin the update process
         by opening Software Update and installing all recommended updates to bring your
         installation current.
Download and install Mac OS X 10.6.8 Update Combo v1.1. You may then open App Store, click on the Purchases icon in the toolbar, and re-download any OS X upgrade you purchased except Mavericks. Since Yosemite has been released the App Store may not let you re-download Mavericks, but it will let you download Yosemite.