Re: Replace line in file based on pattern
On Sun, Jan 02, 2022 at 09:59:08PM -0500, Paul M. Foster wrote:
> Regarding "patch", let's consider a "stock" config file from a fresh install
> (call it NEW), and an existing config which is tweaked for my purposes (call
> it OLD). Assume I want the stock config altered to conform to my
> existing/working installation.
If you're reinstalling after a disk or system failure, you should be
able to drop the config files from your backup onto the system, either
before or after you install the software packages that use those files.
The scenario you seem to be imagining involves reinstalling software
packages and somehow ending up with a *different* version of the software
than you had been running on the failed system. This isn't going
to happen if you were running Debian stable, and you reinstall Debian
stable.
The only way it would be a concern is if you're *not* running Debian
stable, or if you reinstall with something other than Debian stable.
In those cases, well, you're kinda on your own.
> To make patch work, I need a diff file, which I get from diffing OLD and
> NEW. From there, I use patch and the diff to bring NEW to conform to OLD,
> more or less.
I proposed patch because I was imagning a scenario in which you're
administering multiple systems, and you want to make the same change to
the same file on a bunch of systems, BUT the file in question isn't
identical across all systems. Maybe it's got a hostname or an IP address
or something in it, and therefore you are supposed to "edit" the file
with a text editor, find the right line, find the right column, and make
your changes by hand, with immediate visual feedback to tell you that
it looks "right".
As long as the change you're making isn't within a couple lines of the
varying part, the resulting diff should apply cleanly to all your
systems.
patch is also viable for the "stupid Docker user" case that we see all
the time on IRC. In this scenario, the user (I can't even call them an
administrator) has some pre-made Docker image, and they want to
install it repeatedly on the same (virtual) machine, over and over, but
this image hasn't been fully customized for their machine. So they
want to make changes to it after they install it. The same changes.
Every. Single. Time.
(I have no idea why these people don't just make their change to the
image that they're installing from.) (I also have no idea whey they're
installing the same image multiple times. I suspect it's got something
to do with setting up a pristine build environment...?)
Anyway, for that scenario, a diff file applied by patch is safer than
whatever atrocity they write using GNU sed. Then again, for that
scenario, they could also just drop whole files onto the system, rather
than trying to "edit" the image's stock files. Yet they don't seem
to consider either of these solutions. Nope. It's always "how 2 sed??".
Reply to: