Xref: utzoo comp.unix.wizards:9188 comp.unix.questions:7485
Path: utzoo!dciem!nrcaer!scs!spl1!laidbak!att!mtunx!pacbell!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!decwrl!purdue!bu-cs!bzs
From: bzs@bu-cs.BU.EDU (Barry Shein)
Newsgroups: comp.unix.wizards,comp.unix.questions
Subject: Re: grep replacement
Message-ID: <23142@bu-cs.BU.EDU>
Date: 5 Jun 88 15:24:23 GMT
Article-I.D.: bu-cs.23142
References: <136@rubmez.UUCP> <449@happym.UUCP> <7944@alice.UUCP> <8012@brl-smoke.ARPA> <23133@bu-cs.BU.EDU> <8022@brl-smoke.ARPA>
Organization: Boston U. Comp. Sci.
Lines: 82
In-reply-to: gwyn@brl-smoke.ARPA's message of 5 Jun 88 03:30:46 GMT


From: gwyn@brl-smoke.ARPA (Doug Gwyn )
>In article <23133@bu-cs.BU.EDU> bzs@bu-cs.BU.EDU (Barry Shein) writes:
>>Almost, unless the original input was produced by a pipeline, in which
>>case this (putative) post-processor can't help unless you tee the mess
>>to a temp file, yup, mess is the right word.
>
>The proposed tool would be very handy on ordinary text files,
>but it is hard to see a use for it on pipes.  Or, getting back
>to context-grep, what good would it do to show context from a
>pipe?  To do anything with the information (other than stare
>at it), you'd need to produce it again.

What else are context displays for except to stare at (or save in a
file for later staring)?

Are the resultant contexts often the input to other programs? (I know
that 'patch' can take a context input but that's irrelevant, it hardly
needs nor prefers a context diff to my knowledge, it's just being
accomodating so humans can look at the context diff if something
botches.)

Actually, I can answer that in the context of the original suggestion.

The motivation for a context comes in two major flavors:

	A) To stare at (the surrounding context gives a human some
	hint of the context in which the text appeared)

	B) Because the context really represents a multi-line (eg)
	record, such as pulling out every termcap or terminfo entry
	which contains some property but desiring the result to contain
	the entire multiline entry so it could be re-used to create a
	new file.

In either case it's independent of whether the data is coming from a
pipe (as it should be.) Its pipeness may be caused by something as
simple as the data being grabbed across the network (rsh HOST cat foo | ...).

Anyhow, I think it's bad in general to demand the reasoning of why a
selection operator should work in a pipe, it just should (although I
have presented a reasonable argument.) That's what tools are all about.

>There might be some
>use for context-{grep,diff,...} on a stream, but if a separate
>context tool will satisfy 99% of the need, as I think it would,
>as well as provide this capability for other commands "for free",
>it would be a better approach than hacking context into other
>commands.

I think claiming that 99% of the use won't need pipes is unsound, it
should just work with a pipe and any tool which requires passing the
file name and then re-positioning the file just won't, it's violating
a fundamental design concept by doing this (not that in rare cases
this might not be necessary, but I don't see where this is one of them
unless you use the circular argument of it "must be a separate
program".)

The reasoning for adding it to grep would be:

	a) Grep already has its finger on the context, it's right
	there (or could be), why re-process the entire stream/file
	just to get it printed? Grep found the context, why find it
	again?

	b) The context suggestions are merely logical generalizations
	of the what grep already does, print the context of a match
	(it just happens to now limit that to exactly one line.) Nothing
	new conceptually is being added, only generalized.

In fact, if I were to write this context-display tool my first thought
would be to just use grep and try to emit unique patterns (a la TAGS
files) which grep can then re-scan. But grep doesn't quite cut it w/o
this little generalization. I think we're going in circles and this
post-processor is nothing more than a special case of grep or perhaps
cat or sed the way it was proposed (why not just generate sed commands
to list the lines if that's all you want?)

Anyhow, at least we're back to the technical issues and away from
calling anyone who disagrees Neanderthals...

	-Barry Shein, Boston University