Re: [PLUG] Using diff

[Fred Stluka via plug <plug@lists.phillylinux.org>]

Walt,

Yeah, loading a dictionary in Python is a great 1st step towards
lots of useful stuff.

A client of mine had a catastrophe once.  A programmer allowed
cascaded deletes on a database.  So when an employee left and
got deleted from the DB, all her patients got deleted also, and
all of their donations, disbursements, pictures, guestbook entries,
etc.  A major chuck of the DB was gone.

Fortunately, we had good backups.  But hours had passed with
lots of valid donations to other patients and other DB changes
by users around the world.  We couldn't afford to restore from
backup.

Instead we froze the system, and did a dump of the new and old
DBs as text files containing INSERT statements.  Used an approach
like yours to load all the INSERT statements into new and old
Python dictionaries, then looped through them, generating a new
dump file with exactly the right INSERT statements to recreate all
the original data, plus all of the desired changes, but not the
accidental changes.  Re-created the DB from that dump file and
came back on-line.  Total downtime was minimal.  Good stuff!

--Fred
------------------------------------------------------------------------
Fred Stluka -- http://bristle.com -- Glad to be of service!
Open Source: Without walls and fences, we need no Windows or Gates.
------------------------------------------------------------------------

On 5/27/21 9:06 PM, Walt Mankowski via plug wrote:
> I didn't know about the -u option to uniq. Nice!
>
> I think the reason I tend to do them in Perl or Python is that it's
> usually part of a bigger process and I want to do some sort of
> post-processing on the list. The pattern of reading the first file
> into a dictionary, then checking the contents of the second file
> against the dictionary, is useful for all sorts of things.
>
> On Thu, May 27, 2021 at 08:53:08PM -0400, Martin Dellwo via plug wrote:
> > If you know one list contains the other entirely, and neither has its own repetitions, ‘sort first second | uniq -u’ oughta work just fine.
> >
> > Martin Dellwo
> > martin.dellwo@gmail.com
> >
> > > On May 27, 2021, at 8:29 PM, Walt Mankowski via plug <plug@lists.phillylinux.org> wrote:
> > >
> > > I usually end up doing this in Perl or Python. The diff solution is
> > > nice. If you're interested, I've attached a little Perl script I just
> > > whipped up. It has the advantage of not requiring the lists to be
> > > sorted.
> > >
> > > Then I wrote a Python version, too. :)
> > >
> > > Walt
> > >
> > > > On Thu, May 27, 2021 at 07:36:05PM -0400, Michael Lazin via plug wrote:
> > > > Awesome, thanks!   Comm got the job done in a pinch but I am going to try
> > > > diff tomorrow morning.  Thanks again for your help.
> > > >
> > > > Sincerely,
> > > >
> > > > Michael Lazin
> > > >
> > > > > On Thu, May 27, 2021, 6:01 PM Carlos M. Fernández <aremmes@gmail.com> wrote:
> > > > >
> > > > > This has worked for me before:
> > > > >
> > > > > diff -Nau first second | grep '^+'
> > > > >
> > > > > This assumes that first and second are sorted.
> > > > >
> > > > > On Thu, May 27, 2021, 17:37 Michael Lazin via plug <
> > > > > plug@lists.phillylinux.org> wrote:
> > > > >
> > > > > > I used the sort command to make two lists.  One list has everything on
> > > > > > the first list and more.  They are already alphabetically sorted.  I want
> > > > > > to know what is on the second list that is not on the first list.  I am
> > > > > > trying to use diff but perhaps there is a better way.   I tried awk and an
> > > > > > ugly egrep and now I am giving up and asking for help.  Thanks for your
> > > > > > time.
> > > > > >
> > > > > > Sincerely,
> > > > > >
> > > > > > Michael Lazin
> > > > > >
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> > > <not_in_first.pl>
> > > <not_in_first.py>
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