sans-clue has asked for the wisdom of the Perl Monks concerning the following question:

Solaris grep is letting me down and admin rules prevent me from using gnu grep. I have a file that looks

10.1.2.1
myhost
1-4-3-2/0

[download]

I'd like to cat to pipe that file and do a perl regex to print only valid ip addresses.

cat file | perl -.......

and the output would in this case be

10.1.2.1

[download]

I looked around and just found entire scripts. thanks

Replies are listed 'Best First'.
Re: Match Ip Address on cmd line
by NetWallah (Canon) on Sep 09, 2011 at 05:13 UTC
    This 'quick and dirty' regex will work reasonably well for "reasonable" data: 
        perl -ne 'print qq|$1\n| if m/^\s*((?:\d{1,3}\.){3}\d{1,3})\s*$/'

    [download]
    It is tolerant of leading and trailing white-space, but does not check for octets being under 255, or being all zero at the first octet. There are "standard regex" Regexp::Common modules that do a more thorough check for IPv4 validity.

                "XML is like violence: if it doesn't solve your problem, use more."

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[d/l]
      thanks so much, does the trick. what does qq mean ?

      Also, yes I know this isn't a code writing service, but I could not find an 'if m/...' example in a command line, plus I would have never come up with 2 |'s

[reply]

        The things you ask about are partly about style choices.

        Equivalent: 

        do_something() if <condition>;
if (<condition>) { do_something(); }

        [download]

        Equivalent: 

        m[regex]
m|regex|
m/regex/
/regex/

        [download]

        Equivalent: 

        "string-with-expanded-$variables"
qq[string-with-expanded-$variables]
qq/string-with-expanded-$variables/

        [download]
        Using qq// is common on command lines, since the shell itself may require quotes or double-quotes.

        Equivalent: 

        'string-expanding-no-variables'
q[string-expanding-no-variables]
q/string-expanding-no-variables/

        [download]
        All of this can be found in perldoc perlsyn and perldoc perlop.

        --
        [ e d @ h a l l e y . c c ]

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[d/l]
[select]
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Re: Match Ip Address on cmd line
by afoken (Chancellor) on Sep 09, 2011 at 06:07 UTC

    So, what have you tried, where did you fail? Perlmonks is not a code writing service.

    And by the way: Do you want to match only IPv4 addresses or also IPv6 addresses?

    Alexander

    --
    Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
[reply]
Re: Match Ip Address on cmd line
by zentara (Cardinal) on Sep 09, 2011 at 10:08 UTC
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