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It looks like you hosed your bash profile or bashrc

Open up the Preferences menu option.

Click on the Startup Tab

Move the radio button to "Command (complete path)"

Put

"/bin/zsh"

Without the quotes in the box. Close the preferences and hit Apple-N to open a new Terminal window. If this works, type (These files may or may not exist):

rm ~/.bashrc
rm ~/.bash_profile


Then you can probably change the Preference back (assuming you didn't hose the system-wide one)
 
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