If the substitution doesn't match, then the substitution is not performed, so all you need to do is combine the two one liners that you have into one:

perl -pi -e's/^(66.11.10.20)/#$1/g' ips.txt
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Now then, stepping through the list of IP addresses is another issue. I would recommend using a script for this rather than a one liner.

Update: i'm sticking to my case, but this is too much fun. :) Let's say you have 2 text files, one containing the list of all IP addresses (all_IPs.txt) and another containing a smaller list of IP addresses to be commented out in the first text file (decomission_IPs.txt). You could use the shell to create individual strings that contain the Perl one-liners that can in turn be fed back to a shell:

for i in `cat decomission_IPs.txt`; do perl -le $"print 'perl -pi -e \
+'s/^(\Q$i\E)/#\$1/g\' all_IPs.txt' "; done | sh
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L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

Thanks for responding jeffa.

I tried your solution with a for..do loop, but it did not work. It appeared to be running for a small amount of time, but did not do any edits. I tried to run it from ksh and bash, and tried to specify ksh and bash in place of sh, but got no joy.

I thought about trying to do this in xargs, but I too had problems getting it correct. That is why I thought perl might be better.

There are more details in the back story of how I got to this point, but I wasn't sure it was needed for the perl discussion.

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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Thanks for responding Laurent_R.

I don't think I need to worry about the edge cases. I did several steps before I got here, with massaging and normalizing the data. Your solution is like jeffa's. It seemed to execute, but did not edit the file to be worked on. I did add the name of that file to the end of the command you suggested.

I'll keep poking at this as time permits.

True, I forgot to add the name of the file at the end of the command line. Sorry about that.

But I can't say what went wrong with what you are saying in your comments.

Please give full details on what you are trying: exact command line used, sample input files, OS on which you are working, any other thing worth of interest (such as warnings or errors).

Je suis Charlie.

You want bash/ksh do the hard work, just run this:

while read ip;do perl -pi -e s/^/#/ if /$ip/ script_file; done < ip_ad
+dr_file
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Thanks for responding FreeBeerReekingMonk.

I tried your suggestion of a while loop, with redirect in. I am using a test file of 5 ip addresses instead of the whole list. I also have a copy of the original script to see how each solution works. The stdout produced:


Can't open if: No such file or directory.
Can't open /66.22.11.24/: No such file or directory.
Can't open if: No such file or directory.
Can't open /66.22.44.28/: No such file or directory.
Can't open if: No such file or directory.
Can't open /66.22.44.18/: No such file or directory.
Can't open if: No such file or directory.
Can't open /66.33.22.23/: No such file or directory.
Can't open if: No such file or directory.
Can't open /66.33.22.24/: No such file or directory.


The script did get modified, but it put a "#" at the begining of every line, and repeated it 5 times.

hmm, somehow the quotes did not survive, I meant:


while read ip;do perl -pi -e "s/^/#/ if /$ip/" script_file; done < ip_
+addr_file
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Also, if you do not want to match 1.2.3.444 with 1.2.3.4, then \b could help:

while read ip;do perl -pi -e "s/^/#/ if /\b$ip\b/" script_file; done <
+ ip_addr_file
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And yes, it modifies the file immediately, and if you run it multiple times, it will keep adding #'s to each line that needs to be REMarked.
In order to NOT do that, I finally propose:

while read ip;do perl -pi -e "s/^#?/#/ if /\b$ip\b/" script_file; done
+ < ip_addr_file
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Drawbacks: It will iterate over the full file for each IP address. There are other solutions proposed, like the one with map, which is more efficient and faster.

I wouldn't do this as a one-liner, but of course you can. But rather than loop through your IPs and check each of them against the other file (or vice versa), put the IPs in a hash, then go through the other file looking for IP patterns, check them against the hash, and comment them if they're found.

$ cat ips
111.222.333.444
55.66.77.88

$ cat text
Line 1 nothing to comment
Line 2 111.222.333.444 should be commented
Line 3 11.22.33.44 do not comment
Line 4 55.66.77.88 should be commented

$ perl -pe '@l = `cat ips`;chomp @l; %h = map {$_=>1} @l; s/(\d{1,3}\.
+\d{1,3}\.\d{1,3}\.\d{1,3})/$h{$1}?"#$1":$1/e;' <text
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