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Patternmatching IPaddresses

by vyeddula (Acolyte)
on Jun 21, 2013 at 22:33 UTC ( #1040230=perlquestion: print w/ replies, xml ) Need Help??
vyeddula has asked for the wisdom of the Perl Monks concerning the following question:

Pattern matching File

My program #!/usr/bin/perl -w use strict; my $source=shift @ARGV; open(FH,'<',$source) or die "I can't open the file $!\n"; while(<FH>) { s/^(\d*).(\d*)/X.X/g; } close FH;






I want the first 2 octets of other string should also be X and X How to do that?

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Re: Patternmatching IPaddresses
by BrowserUk (Pope) on Jun 21, 2013 at 22:47 UTC
    I want the first 2 octets of other string should also be X and X How to do that?

    Your first step would be to remove the ^ anchoring your regex to the start of the line but that will cause every pair of numbers separated by a dot, (actually, given your regex, any character, you should escape the '.'), which would be all of them result in in everything becoming 'xx.xx.xx.xx';

    So you need to ensure that only the first pair of each quad get modified, so try: s/(?<![0-9.])\d+\.\d+/X.X/g;

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Re: Patternmatching IPaddresses
by choroba (Chancellor) on Jun 21, 2013 at 22:48 UTC
    The other string is not at the beginning of a line. Remove the ^. Also, a dot is a special character in regexes. Backslash it to match literally. You do not need the replaced numbers - no need for capturing parentheses. You do not want the third and fourth numbers to be replaced - you can achieve this by requiring a dot after the numbers to be replaced:
    لսႽ ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
Re: Patternmatching IPaddresses
by 2teez (Priest) on Jun 21, 2013 at 22:53 UTC

    Something like:

    while(<DATA>){ s/[0-9]+\.[0-9]+\./X.X./g; print $_; } __DATA__

    If you tell me, I'll forget.
    If you show me, I'll remember.
    if you involve me, I'll understand.
    --- Author unknown to me
Re: Patternmatching IPaddresses
by johngg (Abbot) on Jun 22, 2013 at 12:34 UTC

    A slightly different approach so as to replace each digit of the masked octets with an 'x' rather than the whole octet with a single 'X' just as an exercise.

    $ perl -Mstrict -Mwarnings -E ' open my $inFH, q{<}, \ <<EOD or die $!; EOD print for map { s{ (\d+\.\d+) (?= (?:\.\d+){2} ) } { do{ my $c = $1; $c =~ tr{0-9}{x}; $c } }xeg; $_; } <$inFH>;' x.x.1.1 x.x.2.2 x.x.3.3 x.x.4.4 $

    I hope this is of interest.



      Replace each digit with an x? Hehe, that reminds me to the winning entry (bottom of page) of the 2008 Underhanded C Contest. Sure, blacking out each digit makes sense if you're doing this on paper with a black pen, or with a scanned image you do not want to OCR, but not much in a string replacement.

Re: Patternmatching IPaddresses
by rjt (Deacon) on Jun 22, 2013 at 23:42 UTC

    You might try explicitly matching either the beginning of the string or a space with (^|\s):

    use 5.014; # For /r regex modifier print s/(^|\s)\d+\.\d+/$1X.X/gr for <DATA>; __DATA__

    Note that if your Perl is older than 5.014, and hence you can not use the /r modifier, you can replace the print() statement with this:

        print map { s/(^|\s)\d+\.\d+/$1X.X/g; $_ } <DATA>;

    If you need stricter validation of your input data, the following regexp will only match lines that have two IP addresses and nothing else:

        s/^\d+\.\d+\.(\d+\.\d+) \d+\.\d+\.(\d+\.\d+)$/X.X.$1 X.X.$2/;

    Note that the /g modifier is not necessary in this case as the regexp covers the entire string.

Re: Patternmatching IPaddresses
by sundialsvc4 (Abbot) on Jun 24, 2013 at 13:00 UTC

    Another very useful CPAN package to get to know is Regexp::Common, which is a kitchen sink collection of “canned,” known good regular-expression patterns, including ones for IP-addresses of all kinds.   Especially useful when you need to validate the contents of a file, or to “future proof” your logic.

    (To fully see what I mean, click on that page, then click on the link to the right of the author’s name in the gray-shadowed line above “Module Version.”   This shows you all of the packages that are part of this one.   Then, if you search for the stringRegexp::Common,” you’ll see about 150 more equally-large ones.

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