#! /bin/sh

# context - dig pattern contexts in text
# Copyright (C) 2010 Matous J. Fialka
# Released under the terms of The MIT License

if [ "$1" = '!' ]
then
	negation='!'
	shift
fi

pattern=${@:-'.*'}

sed "

	/^[^ \t]/b process

:append
	H
	\$ {
		s/.*/\n/
		b process
	}
	d

:process
	x
	/^\$/ b end
	s/^\n//
	/$pattern/${negation} p
	s/.*//

:end
	x
	/^\n\$/ d
	b append
"