Re: [PATCH (topgit) 1/2] Implement setup_pager just like in git

From: Thomas Rast <trast@student.ethz.ch>
Date: Jan 7, 2009, 12:24 UTC
Message-ID: <200901071324.57222.trast@student.ethz.ch>
In-Reply-To: <20090107112754.GA15158@roro3>

Kirill Smelkov wrote:

Show 14 quoted lines

> On Tue, Jan 06, 2009 at 09:32:03PM +0100, martin f krafft wrote:
> > I find this very confusing. Why not simply
> > 
> >   TG_PAGER="${GIT_PAGER:-}"
> >   TG_PAGER="${TG_PAGER:-$PAGER}"
> > 
> > ?
> 
> I find it confusing too, but this is needed because they usually do
> something like this
> 
>     $ GIT_PAGER='' <some-git-command>
> 
> to force it to be pagerless.

[...]

> So I think it would be better to preserve the same semantics for `tg
> patch` callers, though it's a pity that it's hard (maybe I'm wrong ?) to
> see whether an env var is unset.

Admittedly I haven't really studied your patch, but the ${} constructs can in fact tell empty from unset:

  $ EMPTY=
  $ unset UNDEFINED
  $ echo ${UNDEFINED-foo}
  foo
  $ echo ${UNDEFINED:-foo}
  foo
  $ echo ${EMPTY-foo}

  $ echo ${EMPTY:-foo}
  foo

'man bash' indeed says

  When not performing substring expansion, bash tests for a parameter
  that is unset or null; omitting the colon results in a test only for
  a parameter that is unset.

So I suppose you could use

  ${GIT_PAGER-${PAGER-less}}

or similar.

-- 
Thomas Rast
trast@{inf,student}.ethz.ch