% perl kwic.pl a an the
an ostrich
a big bird
the an bird
^D
a BIG bird
a big BIRD
the an BIRD
an OSTRICH
%

##</code><code>##

$i{$x}=1while$x=pop;s/\w+/$i{$&}or$k{$&}.="$`\U$&\E$'"/egwhile<>;print@k{sort keys%k}

##</code><code>##

p={}
i={}
ARGV.each{|x|i[x]=1}.clear
while l=gets;l.gsub(/\S+/){|s|p[s]=''if !p[s];p[s]<<$`+$&.upcase+$'if !i[s]}end
p.sort.each{|x,y|print y}