Q: Terminal unable to run most commands

Recently the terminal app on my iMac has been acting up. When I open the app, it displays the message: "-bash: touch: command not found". I am no longer able to run ruby from the terminal or access irb. Even simple commands such as ls result in "-bash: ls: command not found". The only terminal command that I have been able to run so far is pwd. This iMac is relatively new to me. I purchased it secondhand in December, upgraded the RAM, and restored it using Migration assistant. I have no idea about the purview of this iMac before I purchased it. Yesterday, I did install the 10.11.3 El-Capitan update. Since I have been attempting to use this computer for learning ruby development, right now it seems to be useless for that purpose.