Sub::NoRepeat - Call a subroutine or run a command, but not repeatedly


This document describes version 0.04 of Sub::NoRepeat (from Perl distribution Sub-NoRepeat), released on 2017-07-10.


 use Sub::NoRepeat qw(norepeat);

 # run coderef
 norepeat(code => \&sub1);

 # won't run the same coderef again, noop
 norepeat(code => \&sub1);

 # run coderef because this one is different
 norepeat(code => sub { ... });

 # won't repeat because we use sub1 as key
 norepeat(code => sub { ... }, key => \&sub1);

 # run external command instead of coderef, die on non-zero exit code
 norepeat(command => ['somecmd', '--cmdopt', ...]);

 # will repeat after 24 hours
 norepeat(period => '24h', ...);

 # will repeat after change of day (equals to once daily):
 norepeat(period => 'daily', ...);

 # allows twice daily
 norepeat(period => 'daily', num=>2, ...);


This module is a generalization of the concept of App::norepeat and possibly will supersede it in the future.


Data file is a line-oriented text file, using labeled tab-separated value format ( Each row contains these labels: time (a timestamp either in the format of UTC ISO8601YYYY-MM-DDTHH:MM:SSZ, local ISO8601 YYYY-MM-DDTHH:MM:SS, or Unix timestamp), key (tabs and newlines will be converted to spaces).

The rows are assumed to be sorted chronologically (increasing time).




 norepeat(%args) -> any

Call a subroutine or run a command, but not repeatedly.

This routine allows you to avoid repeat execution of the same subroutine/command. You can customize the key (which command/code are considered the same, the default is the whole command or ref address of subroutine), the repeat period, and some other stuffs.

It works simply by recording the keys and timestamps in a data file (defaults to ~/norepeat.dat, can be customized) after successful execution of commands/subroutines. Commands might still repeat if norepeat fails to record to data file (e.g. disk is full, permission problem).

Keywords: repeat interval, not too frequently, not more often than, at most, once daily, weekly, monthly, yearly, period, limit rate.

This function is not exported by default, but exportable.

Arguments ('*' denotes required arguments):

  • code => code

  • command => array[str]

  • data_file => str

    Set filename to record execution to. Defaults to ~/norepeat.dat.

  • ignore_failure => bool (default: 0)

    By default, if command exits with non-zero status (or subroutine dies), it is assumed to be a failure and won't be recorded in the data file. Another invocation will be allowed to repeat. This option will disregard exit status or trap exception and will still log the data file.

  • key => str

    Key to use when recording event in data file.

    Set key for determining which commands/subroutines are considered the same.

    If you use command, by default it will be the entire command.

    If you use code, by default it will be the ref address of the code, e.g. CODE(0x1655800).

  • now => int

    Assume current timestamp is this value.

  • num => int (default: 1)

    Allow (num-1) repeating during the same period.

    The default (1) allows no repetition during the same period. A value of 2 means allow repeat once (for a total of 2 executions).

  • period => str (default: "forever")

    Set maximum period of repeat detection. The default (when not specified) is forever, which means to never allow repeat, ever, if the same key (command or subroutine) has been run.

    Can either be set to "<number> (sec|min|hour|day|week|month|year)" to express elapsed period after the last run, or "(hourly|daily|weekly|monthly|yearly)" to express no repetition before the named period (hour|day|week|month|year) changes.

    For example, if period is "2 hour" then subsequent invocation won't repeat commands until 2 hours have elapsed. In other words, command/code won't repeat until the next 2 hours. Note that a month is defined as 30.5 days and a year is defined as 365.25 days.

    If period is "monthly", command/code won't repeat execution until the month changes (e.g. from June to July). If you execute the first command on June 3rd, command won't repeat until July 1st. The same thing would happen if you first executed the command/code on June 30th.

    When comparing, local times will be used.

Return value: (any)


Please visit the project's homepage at


Source repository is at


Please report any bugs or feature requests on the bugtracker website

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.


App::norepeat, the CLI version.

Unix cron facility for periodic/scheduling of execution.

Related: modules to limit the number of program instances that can run at a single time: Proc::Govern, Sys::RunAlone.


perlancar <>


This software is copyright (c) 2017, 2015 by

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.