use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new("A\\B")->explain;
__END__
The regular expression:

(?-imsx:A\B)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  A                        'A'
----------------------------------------------------------------------
  \B                       the boundary between two word chars (\w)
                           or two non-word chars (\W)
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new("\\B")->explain;
__END__
The regular expression:

(?-imsx:\B)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  \B                       the boundary between two word chars (\w)
                           or two non-word chars (\W)
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

use re 'debug';
$x = "A\\B";
$y = "Here is A\\B";
print $y =~ /$x/ ? "y" : "n";
__END__
Compiling REx `A\B'
size 4 Got 36 bytes for offset annotations.
first at 1
   1: EXACT <A>(3)
   3: NBOUND(4)
   4: END(0)
anchored "A" at 0 (checking anchored) minlen 1
Offsets: [4]
        1[1] 0[0] 2[2] 4[0]
Guessing start of match, REx "A\B" against "Here is A\B"...
Found anchored substr "A" at offset 8...
Starting position does not contradict /^/m...
Guessed: match at offset 8
Matching REx "A\B" against "A\B"
  Setting an EVAL scope, savestack=3
   8 <Here is > <A\B>     |  1:  EXACT <A>
   9 <Here is A> <\B>     |  3:  NBOUND
                            failed...
Match failed
nFreeing REx: `"A\\B"'
[download]

use re 'debug';
$x = "\\B";
$y = "Here is \\B";
print $y =~ /$x/ ? "y" : "n";
__END__
Compiling REx `\B'
size 2 Got 20 bytes for offset annotations.
first at 1
   1: NBOUND(2)
   2: END(0)
stclass "NBOUND" minlen 0
Offsets: [2]
        1[2] 3[0]
Matching REx "\B" against "Here is \B"
Matching stclass "NBOUND" against "Here is \B"
  Setting an EVAL scope, savestack=3
   1 <H> <ere is \B>      |  1:  NBOUND
   1 <H> <ere is \B>      |  2:  END
Match successful!
yFreeing REx: `"\\B"'
[download]

---

---

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

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:
	&		&
	<		&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.