rem45acp has asked for the wisdom of the Perl Monks concerning the following question:

Hello, I need to match a string like this: "one.two.three". Each title is separated by a ".", and there must be at least one title, but the others are optional. Here is my attempt: 
while ("one.two.three" =~ /([A-Za-z0-9_].+)\.?([A-Za-z0-9_].+)?/g) {
    print "$1\n";
}

[download]
Thank you for any help you can give.

Replies are listed 'Best First'.
Re: Match Optional Groups with 1 Required Group
by BrowserUk (Patriarch) on Feb 04, 2014 at 00:25 UTC 
    print "$_: ", m[^\w+(?:\.\w+){0,2}$] ? 'matched' : 'failed'  
    for qw[ one one.two one.two.three one. one-two ];;
one:  matched
one.two:  matched
one.two.three:  matched
one.:  failed
one-two:  failed

    [download]
    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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[d/l]
      Each title needs at least one character as well.
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        Ah sweet.
[reply]
      This is great. I should have put in the post that there can be an unlimited number of titles, as long as there is one. I'm trying to modify it to allow that: 
      print "$_: ", m[^\w+(?:\.\w+)?$] ? "matched\n" : "failed\n"
    for qw[ one one.two one.two.three four.five.six.seven one. one-two
+ ];

      [download]
[reply]
[d/l]

        ? is zero or one. You need *, which is 0 or more.:

        print "$_: ", m[^\w+(?:\.\w+)*$] ? "matched\n" : "failed\n"
     for qw[ one one.two one.two.three four.five.six.seven one. one-tw
+o ];;
one:  matched
one.two:  matched
one.two.three:  matched
four.five.six.seven:  matched
one.:  failed
one-two:  failed

        [download]
        Each title needs at least one character as well.

        + means 1 or more, so that's covered by \w+

        With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
Re: Match Optional Groups with 1 Required Group
by kcott (Archbishop) on Feb 04, 2014 at 05:51 UTC

    G'day rem45acp,

    Here's another way to do it (I've added a few more tests to ones you posted): 

    #!/usr/bin/env perl -l

use strict;
use warnings;

my @tests = qw{
    one one.two one.two.three four.five.six.seven one. one-two
    .one .one. . .. .@. one.good.egg one.-bad-.egg
};
print "'$_': ", grep(! /^\w+$/, split /\./, $_, -1) ? 'bad' : 'good' f
+or @tests;

    [download]

    Output:

    'one': good
'one.two': good
'one.two.three': good
'four.five.six.seven': good
'one.': bad
'one-two': bad
'.one': bad
'.one.': bad
'.': bad
'..': bad
'.@.': bad
'one.good.egg': good
'one.-bad-.egg': bad

    [download]

    [See split if you're unfamiliar with the 3-argument form.]

    -- Ken

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Re: Match Optional Groups with 1 Required Group
by rem45acp (Novice) on Feb 04, 2014 at 00:22 UTC
    I just realized I could probably use split and then validate each one. However, I'm still open to a regex solution.
[reply]
      Using the split function is exactly what I was going to suggest after having read your original post since it is particularly appropriate for text chunks delimited by separators (although a capturing regex can of course also do it, as shown in the posts below). As a side note, have a look at predefined character classes, such as \w, which can save you quite a bit of typing and make your regexes easier to read and understand.
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