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.1‐2017,  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(1POSIX)