In addition to looking at the documentation linked by kennethk (and also at perlretut; see in particular the section titled 'Looking ahead and looking behind'), perhaps some insight as to the effect of the  \b (and \B) zero-width word (and non-word) boundary assertions can be gained by split-ting one of the OPed example strings on each assertion: 

>perl -wMstrict -le
"my $line2 = 'I:\$AVG\hello.log';
 printf qq{'$_'  } for split /\b/, $line2;
 print qq{\n};
 printf qq{'$_'  } for split /\B/, $line2;
"
'I'  ':\$'  'AVG'  '\'  'hello'  '.'  'log'

'I:'  '\'  '$A'  'V'  'G\h'  'e'  'l'  'l'  'o.l'  'o'  'g'

[download]

In reply to Re^3: regex not matching special char by AnomalousMonk
in thread regex not matching special char by mnooning

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.