RE: libinit idea

> -----Original Message-----
> From: David Chisnall [mailto:theraven_at_FreeBSD.org]
> Sent: Sunday, February 23, 2014 10:18 AM
> To: Allan Jude
> Cc: FreeBSD Current
> Subject: Re: libinit idea
> 
> On 23 Feb 2014, at 18:11, Allan Jude <freebsd_at_allanjude.com> wrote:
> 
> > sysrc solves this nicely, it is in base now, and is great for
> > programmatically adding, removing and changing lines in rc.conf style
> > files. It is also in ports for older versions of FreeBSD where it is
> > not in base.
> 
> The problem is, there is no such thing as an rc.conf style file.  rc.conf
is just a
> shell script.  If you only edit it with sysrc, or you are careful to
preserve the
> structure, then it's fine.

Actually, sysrc is well aware that rc.conf is a shell script and sysrc will
actually
make certain that structure is preserved (regardless of whether you've
placed
shell code in rc.conf or not).

> There is absolutely nothing stopping you, however,
> from writing arbitrarily complex shell scripts inside rc.conf.  Sure, it's
a terrible
> idea to do so, but when has that ever stopped anyone?
> 

When sysrc is told to make a change, it first finds where it needs to make
that
change (/etc/rc.conf or /etc/rc.conf.local or one of other paths mentioned
in
rc_conf_files setting), it will refuse to edit the file *IF* the file
doesn't first
(before editing) pass a shell syntax check (using "sh -n FILE"). After
making the
changes in a temporarily file (produced with mktemp(1)), it again performs
yet
another syntax check (also using "sh -n FILE") to make sure that it
continues to
yield clean syntax.

On top of that, it makes certain not to muck with dynamic assignments. So it
will leave-alone an assignment such as "foo=$( bar )" if told to edit the
variable
foo -- instead opting to add a foo=newvalue after the dynamic assignment
(logic
is simple... sysrc wasn't responsible for putting that dynamic assignment
in, so
it is going to leave it as-is and put the new [static] assignment further
below.

So Allan was absolutely correct in stating that sysrc is for editing
"rc.conf style"
files -- shell scripts really. In essence, sysrc is actually a shell script
modifying
utility that takes extreme special care to rely on the fact that rc.conf
*is* a
shell script.

> An rc-replacement could enforce this by only accepting purely declarative
files
> for configuration, guaranteeing that if they were syntactically valid they
would
> also be machine editable, no matter what the user does to them.
> 

sysrc does this for you.
-- 
Devin

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