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Multiline Regex

by Cosmivalin (Initiate)
on Feb 15, 2001 at 23:30 UTC ( [id://58698]=perlquestion: print w/replies, xml ) Need Help??

Cosmivalin has asked for the wisdom of the Perl Monks concerning the following question:

<html> <head> <meta http-equiv="Content-Language" content="en-us"> <meta http-equiv="Content-Type" content="text/html; charset=windows-1252"> <title>New Page 1</title> </head> <body>

Hi all, I have what's probably a simple question, but it stumping me. I am trying to develop a multi-line regex that will look through a text file and look for any lines that start with an ipaddress, but also the next line must contain "OS Type: unknown" and then insert a carriage return in front of the line with the ip address above that. I cant insert a CR in front of just any line that starts with an ipaddress. i.e.

bogus info

this could be anything

OS Type: unknown

filler information

OS Type: unknown


Any assistance would be appreciated... Thanks!

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Re: Multiline Regex
by kilinrax (Deacon) on Feb 15, 2001 at 23:37 UTC
    Asumming I've understood your question correctly, something like the following?
    #!/usr/bin/perl -w use strict; my $data = join '', <DATA>; $data =~ s|(?=^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\nOS Type: unknown$)| +\n|gm; print $data; exit(1); __DATA__ bogus info this could be anything OS Type: unknown filler information OS Type: unknown
      Although the right solution is to use multiline mode, your code doesn't do anything as the test on the regex reveals. See here:
      #!/usr/bin/perl -w use strict; my $data = join '', <DATA>; if($data =~ s|(?=^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\nOS Type: unknown +$)|\n|gm) { print "yes, it worked!"; } #print $data; exit(1); __DATA__ bogus info this could be anything OS Type: unknown filler information OS Type: unknown
      The above code returns nothing, meaning that the regex never does the substitution. From a quick rereading of the algorithm, it looks like he is trying to do the following:
      1. Read through the file
      2. find lines that start with IP addresses
      3. ASK if the next line following it has some specific text
      4. write an extra space BETWEEN the IP address line and the specific text line
      I may be wrong, as the spec. was pretty poorly written. A quick command line example that does this is as follows:
      perl -e "$q = qq(the brown dog\n is hailing a cab); if (($q=~m/\n(.*)/ +mg) && ($1 eq q( is hailing a cab))) { print qq(\n$1;)} else {print ' +no luck buddy.';}"

      Celebrate Intellectual Diversity

        Actually, the regex "mostly works".

        The problem with this regex is that the DATA does not have an immediate newline following it (there is a space). If the space is removed - or a simple (.+)? is added between the IP match and the newline, the first regex works fine. I'll leave someone else to do the benchmarks :-)

        That's of course, if the original poster wants the new line before the line with the IP

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