Where is the hash command documentation?

Question

When I type man hash it shows me man builtin.

I'm trying to understand this line:

hash -r 2>/dev/null || true

What hash -r does and what it returns.

Context:

export PATH="$PWD/bin:$PATH"
hash -r 2>/dev/null || true

https://github.com/rbenv/rbenv/wiki/Understanding-binstubs#adding-project-specific-binstubs-to-path

Answer 1

hash is a shell builtin.

If you are using bash, check:

help hash

For your convenience, here it is:

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.

Options:
  -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
Arguments:
  NAME              Each NAME is searched for in $PATH and added to the list
            of remembered commands.

Exit Status:
Returns success unless NAME is not found or an invalid option is given.

For other shells, check the usual place for builtins. For example, for zsh, check:

man zshbuiltins

---

What hash -r does and what it returns.

hash -r removes all remembered locations from the hash table and it returns success.

Answer 2

hash is a standardized shell builtin and hash -r resets the current path hash that is used to locate comands in PATH.

Calling hash -r after setting PATH is however not needed as changing PATH automatically resets the current command hashing. This is true for the Bourne Shell and for ksh and I would expect other shells to behave the same way.