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 2.9.1.4 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 and functions shall not be reported by hash.

OPTIONS

The hash utility shall conform to XBD 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 the search does not find utility, it is unspecified whether or not this is treated as an error. 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 XBD 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

^[XSI] Determine the location of messages objects and message catalogs.

PATH

Determine the location of utility, as described in XBD 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. This list shall be cleared when the contents of the PATH environment variable are changed.

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.

APPLICATION USAGE

This utility is required to be intrinsic. See 1.7 Intrinsic Utilities for details.

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 -exec 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

If this utility is directed to display a pathname that contains any bytes that have the encoded value of a <newline> character when <newline> is a terminator or separator in the output format being used, implementations are encouraged to treat this as an error. A future version of this standard may require implementations to treat this as an error.

SEE ALSO

2.9.1.4 Command Search and Execution

XBD 8. Environment Variables, 12.2 Utility Syntax Guidelines

CHANGE HISTORY

First released in Issue 2.

Issue 7

The hash utility is moved from the XSI option to the Base.

POSIX.1-2008, Technical Corrigendum 1, XCU/TC1-2008/0093 [241] is applied.

Issue 8

Austin Group Defect 248 is applied, changing a command line in the APPLICATION USAGE section.

Austin Group Defect 251 is applied, encouraging implementations to report an error if a utility is directed to display a pathname that contains any bytes that have the encoded value of a <newline> character when <newline> is a terminator or separator in the output format being used.

Austin Group Defect 854 is applied, adding a note to the APPLICATION USAGE section that this utility is required to be intrinsic.

Austin Group Defect 1063 is applied, clarifying that functions are not reported by hash, and that the list of remembered locations is cleared when the contents of PATH are changed.

Austin Group Defect 1122 is applied, changing the description of NLSPATH .

Austin Group Defect 1460 is applied, making it explicitly unspecified whether or not hash reports an error if it cannot find utility.