Re: regex quirks

"'Vratislav Podzimek' via help-cfengine" <[email protected]> Tue, 03 Aug 2021 13:22:45 +0200

Newsgroups	gmane.comp.sysutils.cfengine.general
Message-ID	<[email protected]>

On Wed, 2021-07-28 at 07:29 -0700, Xander Cage wrote:
> 
> hey,
> 
> i'm toying  around in making a bundle for crontab editing (add,
> modify, remove) and regex is
> beginning to bite me.
> 
> i got an "informational" message that my pattern matching skills are
> downlevel.
> 
> /var/cfengine/bin/cf-agent -KI -f ./nmon_cron_test.cf
>     info: Promised replacement '0 0 * * * /usr/bin/nmon -F
> /var/log/nmon/`hostname`_`date +'\%y\%m\%d_\%H\%M'`.nmon -s 300 -c
> 288 1>/dev/null 2>/dev/null' for pattern '^.*/usr/bin/nmon -F.*$' is
> not properly convergent while editing '/var/spool/cron/crontabs/root'
>     info: Because the regular expression '^.*/usr/bin/nmon -F.*$'
> still matches the end-state replacement string '0 0 * * *
> /usr/bin/nmon -F /var/log/nmon/`hostname`_`date
> +'\%y\%m\%d_\%H\%M'`.nmon -s 300 -c 288 1>/dev/null 2>/dev/null'

The 'info' message explains what the problem is -- the anchor regular
expression matches the replacement string. That means the promise
doesn't converge -- it will make a change every time it is evaluated.
That's generally considered a bad pattern in CFEngine (and any engine
based on state specification instead of action specification).

You can ignore the message or, ideally, change the regex to only match
the undesired state.

Thanks.

--
Vratislav

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