I thought I had a reasonable handle on regexes but occasionally problems shatter my confidence. I am trying to match Roman Numerals in the range i to xxxix. The numerals maybe preceded by a left bracket and maybe followed by i. a period (ii) a right bracket or (iii). a right bracket followed by a period. The entire pattern is always terminated with a space.
It all appears to work ok except when the string being searched comprises just a single space, whence it is (incorrectly IMHO) matched.
The part of the pattern to the left of the cluster that contains the space that is matched (ie the roman numeral cluster) has a quantifier of {1,1}, so I really don't undertand, if there are no valid characters in the string before the space, why the space should be matched.
Any help would be greatly appreciated.
This code outputs Matched ' ' in ' '



use strict;
#use re 'debug';

{
  my ($rv, $linestr, $pattern);
  
  $linestr = ' ';
  $pattern = '^\({0,1}(((ix)|(iv))|(x{0,3}((ix)|(iv)))|(x{0,3}(v{0,1}i
+{0,3}))){1,1}((\)\. )|(\) )|(\. )|( )){1,1}';

 if( $linestr =~ m/$pattern/i)
  {
    print ("Matched '$&' in '$linestr'\n");
  }
  else
  {
      print ("Not matched\n");
  }
}

[download]

In reply to Pattern Matching by davidas

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.