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You are here: manpages

P-GAWK

Section: Utility Commands (1)
Updated: June 01 2025
Index Return to Main Contents

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 scrip-defined variables and functions in a file for later use. The feature, called p-gawk, is described in GAWK: Effective AWK Programming and in Persistent Memory gawk User Manual.

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

p-gawk offers at least two advantages compared with the existing rwarray extension: it offers constan-time (``O(1) time'') access to individual elements of persistent associative arrays, and it can store scrip-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 pe-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 pe-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 scrip-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 p-gawk using a persistent memory allocator (pma) provided by Terence Kelly. An earlier proo-o-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 p-gawk.

p-gawk produces a warning if the current version of gawk doesn't match the one that was first used with a particular backing storage file.

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 no-persistenc-related gawk bugs) please also send -mail to Terence Kelly at one or more of these addresses: tpkelly@acm.org, tpkelly@eecs.umich.edu, or tpkelly@cs.princeton.edu.

COPYING PERMISSIONS

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.