HASH(1P) POSIX Programmer's Manual HASH(1P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
hash — remember or report utility locations
The hash utility shall affect the way the current shell environment
remembers the locations of utilities found as described in Section
220.127.116.11, 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 hash utility shall conform to the Base Definitions volume of
POSIX.1‐2008, 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:
utility The name of a utility to be searched for and added to the
list of remembered locations. If utility contains one or more
<slash> characters, the results are unspecified.
The following environment variables shall affect the execution of hash:
LANG Provide a default value for the internationalization vari‐
ables that are unset or null. (See the Base Definitions vol‐
ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
ables 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 internationalization variables.
LC_CTYPE 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
NLSPATH Determine the location of message catalogs for the processing
PATH Determine the location of utility, as described in the Base
Definitions volume of POSIX.1‐2008, Chapter 8, Environment
The standard output of hash shall be used when no arguments are speci‐
fied. Its format is unspecified, but includes the pathname of each
utility in the list of remembered locations for the current shell envi‐
ronment. 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 sepa‐
rate 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 environ‐
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 applica‐
tions, but may provide a performance improvement on a few implementa‐
tions; normally, the hashing process is included by default.
Section 18.104.22.168, Command Search and Execution
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
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IEEE/The Open Group 2013 HASH(1P)