Linux weird problem touch : command not found?

You probably temporarily messed up your path. It may be enough to do:

exec /bin/bash

Then you can try touch, etc. to make sure things are normal.

If that doesn't work, the PATH definition is wrong in one of your system files.

Try to find the command manually. It will be a file named touch and on my current system it is /bin/touch. You can find it by with locate touch or even find / -name touch. If you find it with locate and it isn't where it says that it should be, that could mean that it was recently moved or deleted.

Once you find the command, make sure that it is in your PATH with echo $PATH. If all this works, try specifying the path and command together (i.e. /bin/touch foo). You may also want to check your aliases to see if there is anything there messing things up.

As an observation, you mention that vi isn't working either. In my system, both vi and touch are in /bin and not /usr/bin. Check to see if you are able to run other commands from there.

I made the mistake of overriding my PATH in a script;

while read -r PATH; do
  touch "${PATH}";
done < <(git diff-tree --no-commit-id --name-only -r "${COMMIT_ID}")

The read -r PATH bit cleared the path to the touch binary.

Fix was a simple rename:

while read -r GIT_PATH; do