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HASH(1P) POSIX Programmer's Manual HASH(1P)
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
hash [utility...]
hash -r
The hash utility shall affect the way the current shell
environment remembers the locations of utilities found as
described in Section 2.9.1.1, 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
POSIX.1‐2017, 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.
Not used.
None.
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 POSIX.1‐2017, Section 8.2,
Internationalization 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 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).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
NLSPATH 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 POSIX.1‐2017, Chapter 8,
Environment Variables.
Default.
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.
None.
None.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
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:
PATH="$PATH"
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.
None.
None.
None.
Section 2.9.1.1, Command Search and Execution
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 HASH(1P)
Pages that refer to this page: set(1p), type(1p)
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