How to undo alias, PATH=$PATH:./Test - (Unix)

Question

1.) In a terminal when we make an alias for any command line,the life of that alias is as long as the terminal is open.

alias new_command=old_command

example: alias dog=cat

But can we explicitly undo the alias command? i.e undo the alias assigned to that command without closing the terminal.

2.) Also when we do something like PATH=$PATH:.:/Test

We add the files to that directory wherein all the command are stored.How do we undo this? One way of doing it is by closing the terminal,whats the other way?

I'm new to Unix ,please help. Correct me if i'm wrong

Answer 1

1) unalias dog

2) This will remove the lastmost directory from your path: PATH=${PATH%:*}. Repeat it as needed for however many bad entries you've got.

Answer 2

1) You mean like unalias ?