NAME

       persistent memory gawk - persistent data and functions

SYNOPSIS

       truncate -s size heap.pma
       export GAWK_PERSIST_FILE=heap.pma
       gawk ...

       truncate -s size heap.pma
       GAWK_PERSIST_FILE=heap.pma gawk ...

       truncate -s size heap.pma
       alias pm='GAWK_PERSIST_FILE=heap.pma'
       pm gawk ...                       # succinct

       unset GAWK_PERSIST_FILE   # disable persistence

       export GAWK_PERSIST_FILE=other_heap.pma  # change heap

       rm heap.pma               # delete heap

DESCRIPTION

       Gawk  5.2  and  later  supports  a  persistent memory feature that can store script-defined variables and
       functions in a file for later use.  The feature, called pm-gawk, is  described  in  GAWK:  Effective  AWK
       Programming and in Persistent Memory gawk User Manual.

       pm-gawk  is  activated  by passing to gawk the name of an initially empty (all-zero-bytes) heap file, via
       the environment variable GAWK_PERSIST_FILE.  pm-gawk retains script-defined variables  and  functions  in
       the heap file for use in subsequent gawk invocations.

       pm-gawk  offers at least two advantages compared with the existing rwarray extension: it offers constant-
       time (``O(1) time'') access to individual elements of persistent associative arrays,  and  it  can  store
       script-defined functions in addition to variables.

EXAMPLES

       Demonstrate persistent variables:
              $ truncate -s 1G heap.pma            # create heap file
              $ export GAWK_PERSIST_FILE=heap.pma  # "ambient" env var
              $ gawk 'BEGIN { print ++i }'
              1
              $ gawk 'BEGIN { print ++i }'
              2
              $ gawk 'BEGIN { print ++i }'
              3

       To pass the environment variable on per-command basis:
              $ unset GAWK_PERSIST_FILE
              $ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'
              4
              $ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'
              5
              $ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'
              6

       To reduce visual clutter of per-command environment variable passing:
              $ alias pm='GAWK_PERSIST_FILE=heap.pma'
              $ pm gawk 'BEGIN { print ++i }'
              7
              $ pm gawk 'BEGIN { print ++i }'
              8

       To refrain from activating persistence:
              $ unset GAWK_PERSIST_FILE
              $ gawk 'BEGIN { print ++i }'
              1
              $ gawk 'BEGIN { print ++i }'
              1

       To permanently ``forget'' the contents of the heap file:
              $ rm heap.pma

ENVIRONMENT VARIABLES

       GAWK_PERSIST_FILE  contains  the  name  of  a  heap file where script-defined variables and functions are
       stored.  If this environment variable is not visible to gawk, the persistence feature  is  not  activated
       and gawk behaves in its traditional manner.

VERSION INFORMATION

       Persistent memory gawk was first released in gawk 5.2.

AUTHORS

       Arnold  Robbins,  the  maintainer  of gawk, implemented pm-gawk using a persistent memory allocator (pma)
       provided by Terence Kelly.  An earlier proof-of-concept prototype of persistent  gawk  was  developed  by
       Haris Volos, Zi Fan Tan, and Jianan Li using a fork of the official gawk sources.

CAVEATS

       The  GNU/Linux CIFS filesystem is known to cause problems for the persistent memory allocator. Do not use
       a backing file on such a filesystem with pm-gawk.

BUG REPORTS

       Follow the procedures in GAWK: Effective AWK Programming and in Persistent Memory gawk User Manual.   For
       suspected bugs related to persistence (as opposed to other non-persistence-related gawk bugs) please also
       send  e-mail to Terence Kelly at one or more of these addresses: tpkelly@acm.org, tpkelly@eecs.umich.edu,
       or tpkelly@cs.princeton.edu.

SEE ALSO

       gawk(1), GAWK: Effective AWK Programming, and Persistent Memory gawk User Manual.  The two manuals should
       be available in the Info subsystem if Info installed on your system.

       See https://web.eecs.umich.edu/~tpkelly/pma/ for the latest source code and manual.

COPYING PERMISSIONS

       Copyright © 2022 Terence Kelly.

       Permission is granted to make and distribute verbatim copies of this manual page provided  the  copyright
       notice and this permission notice are preserved on all copies.

       Permission  is  granted to copy and distribute modified versions of this manual page under the conditions
       for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a
       permission notice identical to this one.

       Permission is granted to copy and distribute translations of this  manual  page  into  another  language,
       under  the  above conditions for modified versions, except that this permission notice may be stated in a
       translation approved by the Foundation.

Free Software Foundation                           Nov 17 2022                                        PM-GAWK(1)