The hash utility shall affect the way the current shell environment
remembers the locations of utilities found as described in Command Search
and Execution . Depending on the arguments specified, it shall add utility
locations to its list of remembered locations or it shall purge the contents
of the list. When no arguments are specified, it shall report on the contents
of the list.
Utilities provided as built-ins to the shell shall not be reported by
The following environment variables shall affect the execution of hash:
Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
If set to a non-empty string value, override the values of
all the other internationalization variables.
Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to standard error.
Determine the location of message catalogs for the
processing of LC_MESSAGES.
Determine the location of utility, as described in
the Base Definitions volume of IEEE Std 1003.1-2001, Chapter
8, Environment Variables.
The standard output of hash shall be used when no arguments are
specified. Its format is unspecified, but includes the pathname of each
utility in the list of remembered locations for the current shell environment.
This list shall consist of those utilities named in previous hash
invocations that have been invoked, and may contain those invoked and found
through the normal command search process.
Since hash affects the current shell execution environment, it is always
provided as a shell regular built-in. If it is called in a separate utility
execution environment, such as one of the following:
nohup hash -rfind . -type f | xargs hash
it does not affect the command search process of the caller's environment.
The hash utility may be implemented as an alias-for example, alias-t -, in which case utilities found through normal command
search are not listed by the hash command.
The effects of hash-r can also be achieved portably by resetting
the value of PATH ; in the simplest form, this can be:
The use of hash with utility names is unnecessary for most
applications, but may provide a performance improvement on a few
implementations; normally, the hashing process is included by default.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html