Re: regex quirks

when i negate the regex the info message is gone, but no edits are 
done...causality dilemma. 

bundle edit_line itsv_modify_cron_line ( _find, _replace )
# @brief modify lines matching a regular expression eg. ".*\/usr\/bin\/nmon 
-F \/var\/log\/nmon.*1.*"
# @param _find The regular expression that the lines need to match
# @param _replace String to substitute `_find` with
{

  replace_patterns:

   "^(?!$(_find))$"
     replace_with => value("$(_replace)");

#   delete_lines:
#
#      "^($(_find))$";
#
#   insert_lines:
#
#     "$(_replace)";


}


On Tuesday, August 3, 2021 at 1:22:49 PM UTC+2 [email protected] 
wrote:

> 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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