hash

hash is a shell built-in that manages the hash table of recently executed commands. The shell uses this table to remember the full paths of commands, avoiding repeated PATH searches.When a command is executed, the shell stores its path in the hash table. Subsequent invocations use the cached path, improving performance.

$ # View hash table
hash

# Clear after installing new software
hash -r

# Check where a command is hashed
hash -t python

# List all hashed commands
hash -l

-r

Clear hash table.

Add path for name.

Delete name from hash.

Print path for name.

List in reusable format.

Shell built-in; behavior and available options vary by shell (bash, zsh, ksh each implement their own version). The hash table becomes stale if a hashed command's file is moved or removed. Run `hash -r` after installing software or modifying PATH. Only affects the current shell session, not child processes.

hash has been part of Unix shells since the Bourne shell. POSIX only mandates the `-r` option; bash extends it with `-p`, `-d`, `-t`, and `-l` for finer control over the command path cache.

type(1), which(1), whence(1), command(1)

Documentation