hash - remember or report utility locations
hash [utility...] hash -r
The hash utility affects 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 adds utility locations to its list of remembered locations or it purges the contents of the list. When no arguments are specified, it reports on the contents of the list.
Utilities provided as built-ins to the shell are not reported by hash.
The hash utility supports the XBD specification, Utility Syntax Guidelines .
The following option is supported:
- Forget all previously remembered utility locations.
The following operand is supported:
- The name of a utility to be searched for and added to the list of remembered locations. If utility contains one or more slashes, the results are unspecified.
The following environment variables affect the execution of hash:
- Provide a default value for the internationalisation variables that are unset or null. If LANG is unset or null, the corresponding value from the implementation-dependent default locale will be used. If any of the internationalisation variables contains an invalid setting, the utility will behave as if none of the variables had been defined.
- If set to a non-empty string value, override the values of all the other internationalisation variables.
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single- 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.
- Determine the location of message catalogues for the processing of LC_MESSAGES .
- Determine the location of utility, as described in the XBD specification, Environment Variables .
The standard output of hash is 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 consists 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.
Used only for diagnostic messages.
The following exit values are 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:it will not affect the command search process of the caller's environment.
nohup hash -r find . -type f | xargs hash
The hash utility may be implemented as an alias, for example, alias -t -, in which case utilities found through normal command search will not be 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 applications, but may provide a performance improvement on a few implementations; normally, the hashing process is included by default.
Command Search and Execution.