Re: cat and pipelines, mostly (was Re: Delete all after a pattern)

[David <bouncingcats@gmail.com>]

On Sun, 1 Sep 2019 at 00:39, The Wanderer <wanderer@fastmail.fm> wrote:
> On 2019-08-31 at 10:07, Roberto C. Sánchez wrote:
> > On Sat, Aug 31, 2019 at 09:26:49AM -0400, The Wanderer wrote:
> >> On 2019-08-31 at 09:02, Roberto C. Sánchez wrote:
> >>
> >>> The only time you need to change the syntax is to add something
> >>> before sed.  But then, that's why shells have I/O redirection:
> >>>
> >>> (sed 's/config=.*$/config=/g' | tr -d '=') <~/test.txt
> >>>> ~/other_test.txt
> >>
> >> This is *far* more complicated and messy, both syntactically and to
> >> type in, than just having cat at the beginning of a pipeline.
> >>
> > That's quite a stretch.
> >
> > Your way:
> >
> > cat ~/test.txt | sed 's/config=.*$/config=/g' | tr -d '='
> > >~/other_test.txt
> >
> > A better way:
> >
> > (sed 's/config=.*$/config=/g' | tr -d '=') <~/test.txt
> > >~/other_test.txt

[...]

> I think this is a case of minds working differently.

[...]

> In that case, I fail to see the benefit. As far as I can tell, saving a
> process is the entire sum-total benefit of avoiding the use of cat in
> this type of context.

For readers interested in this topic, here's a thorough coverage
of many aspects of it:
http://mywiki.wooledge.org/BashFAQ/119
http://mywiki.wooledge.org/BashPitfalls#cat_file_.7C_sed_s.2Ffoo.2Fbar.2F_.3E_file
https://backreference.org/2011/01/29/in-place-editing-of-files/
http://mywiki.wooledge.org/BashFAQ/021