I agree with jeffa that this is getting a bit complicated for a one-liner. But a one-liner does not have to be only one line. Or you might want to call it a "two-liner". This compiles cleanly, but I haven't really tested it with actual data. Besides, it certainly does not take care of edge cases. This is just a clue for a possible pure Perl (no Bash) solution. 
perl -pi -e 'BEGIN{ local @ARGV = ("IP_addr.txt"); %IP = map {$_ => 1;
+} <>; }
      $_ = "#" . $_  if /((\d{1,3}\.){3}(\d{1,3}))/ and exists $IP{$1}
+;'

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Je suis Charlie.

In reply to Re: one liner with separate input file? by Laurent_R
in thread one liner with separate input file? by MrGibbs

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