hash is a built-in command of the
bash shell. For a summary of what it does you can type
help hash at the shell prompt:
$ help hash
hash: hash [-lr] [-p pathname] [-dt] [name ...]
Remember or display program locations.
Determine and remember the full pathname of each command NAME. If
no arguments are given, information about remembered commands is displayed.
-d forget the remembered location of each NAME
-l display in a format that may be reused as input
-p pathname use PATHNAME as the full pathname of NAME
-r forget all remembered locations
-t print the remembered location of each NAME, preceding
each location with the corresponding NAME if multiple
NAMEs are given
NAME Each NAME is searched for in $PATH and added to the list
of remembered commands.
Returns success unless NAME is not found or an invalid option is given.
hash remembers program locations, and
hash -r forgets them.