The /usr/bin/hash utility affects the way the current shell environment remembers the locations of utilities found. Depending on the arguments specified, it adds utility locations to its list of remembered locations or it purges the contents of the list. When no arguments are specified, it reports on the contents of the list.

Utilities provided as built-ins to the shell are not reported by hash.

For each name, the location in the search path of the command specified by name is determined and remembered by the shell. The -r option to the hash built-in causes the shell to forget all remembered locations. If no arguments are given, hash provides information about remembered commands. The Hits column of output is the number of times a command has been invoked by the shell process. The Cost column of output is a measure of the work required to locate a command in the search path. If a command is found in a "relative" directory in the search path, after changing to that directory, the stored location of that command is recalculated. Commands for which this will be done are indicated by an asterisk (*) adjacent to the Hits information. Cost will be incremented when the recalculation is done.

rehash recomputes the internal hash table of the contents of directories listed in the path environmental variable to account for new commands added.

unhash disables the internal hash table.

hashstat prints a statistics line indicating how effective the internal hash table has been at locating commands (and avoiding execs). An exec is attempted for each component of the path where the hash function indicates a possible hit and in each component that does not begin with a '/'.

For each name, the location in the search path of the command specified by name is determined and remembered by the shell. If no arguments are given, hash provides information about remembered commands.