Since that you are checking first and last characters with $b[$i-($m-1)] and $b[$i] respectively, your in-between characters should be 
@b[$i-($m-2)..$i-1]

[download]
That is,
say 
$i = 10;
$m = 8;

[download]
Your first character according to your check should be in $b[3] and last character should be in $b[10]. So the in-between characters should be 
@b[4..9]

[download]
But you are checking 3..10 again.
From your code, for(my $j=($i-($m-1));$j<=$i;$j++)
I guess this should be 
for(my $j=($i-($m-2));$j<=$i-1;$j++)
#or
for(my $j=($i-($m-2));$j<$i;$j++)

[download]
Does this help you.
Thanks..

In reply to Re^3: doubt in string matching. by Mandrake
in thread doubt in string matching. by heidi

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.