TIMTOWTDI: 

> cat a
aa
ab
aaa
aaaa
> cat b
ab
bb
bbb
bbbb
> perl -ne 'BEGIN{ $v=1 ; @A=@ARGV }; chomp; $c{$_}+=$v; $v=-1 if eof;
+ END { foreach (sort keys %c) { print $c{$_}>=0 ? "$A[0] " : "- "; pr
+int $c{$_}<=0 ? "$A[1] " : "- "; print " : $_\n" }}' a b
a -  : aa
a -  : aaa
a -  : aaaa
a b  : ab
- b  : bb
- b  : bbb
- b  : bbbb

[download]
I am sure, this can be golfed...

In reply to Re: One liner to compare to lists and print the ID's in common by Perlbotics
in thread One liner to compare to lists and print the ID's in common by ZWcarp

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