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.1‐2008, 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.1‐2008,  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.1‐2008, 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.1‐2008, 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, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .