HASH(P) POSIX Programmer's Manual HASH(P)
hash - remember or report utility locations
The hash utility shall affect the way the current shell environment remembers the loca-
tions 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 hash.
The hash utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001,
Section 12.2, Utility Syntax Guidelines.
The following option shall be supported:
-r Forget all previously remembered utility locations.
The following operand shall be supported:
The name of a utility to be searched for and added to the list of remembered loca-
tions. If utility contains one or more slashes, the results are unspecified.
The following environment variables shall affect the execution of hash:
LANG 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, Inter-
nationalization Variables for the precedence of internationalization variables used
to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all the other interna-
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 argu-
Determine the locale that should be used to affect the format and contents of diag-
nostic messages written to standard error.
Determine the location of message catalogs for the processing of LC_MESSAGES .
PATH 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.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
The following sections are informative.
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 -r
find . -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.
Command Search and Execution
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 HASH(P)