HASH
Section: POSIX Programmer's Manual (1P)
Updated: 2013
Index
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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.
NAME
hash
--- remember or report utility locations
SYNOPSIS
hash [utility...]
hash -r
DESCRIPTION
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.
OPTIONS
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.
OPERANDS
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.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
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.1-2008,
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.1-2008,
Chapter 8, Environment Variables.
ASYNCHRONOUS EVENTS
Default.
STDOUT
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.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
- 0
-
Successful completion.
- >0
-
An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
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.
EXAMPLES
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.9.1.1,
Command Search and Execution
The Base Definitions volume of POSIX.1-2008,
Chapter 8,
Environment Variables,
Section 12.2,
Utility Syntax Guidelines
COPYRIGHT
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
Electrical 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 .
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- OPERANDS
-
- STDIN
-
- INPUT FILES
-
- ENVIRONMENT VARIABLES
-
- ASYNCHRONOUS EVENTS
-
- STDOUT
-
- STDERR
-
- OUTPUT FILES
-
- EXTENDED DESCRIPTION
-
- EXIT STATUS
-
- CONSEQUENCES OF ERRORS
-
- APPLICATION USAGE
-
- EXAMPLES
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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