From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Thu, 12 Mar 2015 09:46:31 -0700
To: 9fans@9fans.net
Message-ID: <8f07dd60b7c8ad5c85e3b6ed8ac18a37@brasstown.quanstro.net>
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Subject: [9fans] fun with rc
Topicbox-Message-UUID: 49560fc4-ead9-11e9-9d60-3106f5b1d025

so an interesting problem i run into from time to time is separately comp=
uting
the files added to and deleted from a directory in a shell script.  uniq =
doesn't
work for this.  certainly one can loop over two lists of files and do thi=
s easily,
but that seems dull and tedious.

but as it turns out, one can compute the deleted and added files relative=
ly
efficiently with diff in two steps.  obviously uniq -d gives us the union=
, so

	fn =E2=88=A9 {echo $$1 $$2 | sed 's/ /\n/g' | sort | uniq -d}

and uniq -u gives us not union

	fn not=E2=88=A9 {echo $$1 $$2 | sed 's/ /\n/g' | sort | uniq -u}

but then we can compuete the "difference" (relative complement) we want
with

	fn listminus {c=3D`{=E2=88=A9 $1 $2} not=E2=88=A9 c $1}

so then

	echo 'added=3D('  `{listminus old new} ')'
	echo 'deleted=3D('  `{listminus new old} ')'

he!  such fun with rc.

this is available now in 9atom.

- erik