pm-gawk - Man Page

persistent data and functions


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


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.


Demonstrate persistent variables:

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

To pass the environment variable on per-command basis:

$ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'
$ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'
$ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'

To reduce visual clutter of per-command environment variable passing:

$ alias pm='GAWK_PERSIST_FILE=heap.pma'
$ pm gawk 'BEGIN { print ++i }'
$ pm gawk 'BEGIN { print ++i }'

To refrain from activating persistence:

$ gawk 'BEGIN { print ++i }'
$ gawk 'BEGIN { print ++i }'

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.


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.


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:,, or

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 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.


Nov 17 2022 Free Software Foundation Utility Commands