HASH(1)                    POSIX Programmer's Manual                   HASH(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.1-2017, 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.1-2017, 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.

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.1-2017, 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 1003.1-2017, 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(1)
