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 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 XBD Utility Syntax Guidelines .
The following option shall be supported:
- 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 locations. If utility contains one or more <slash> characters, the results are unspecified.
The following environment variables shall affect the execution of hash:
- Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- 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 error.
- [XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.
- Determine the location of utility, as described in XBD 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:
- Successful completion.
- An error occurred.
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.
Command Search and Execution
XBD Environment Variables, Utility Syntax Guidelines
First released in Issue 2.
The hash utility is moved from the XSI option to the Base.
POSIX.1-2008, Technical Corrigendum 1, XCU/TC1-2008/0093  is applied.
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