Re^3: regex not matching special char

Am I asking too much of Perl regex?

;) No, is Perl regex asking too much by asking you to know what you're asking for ? *zing*

Luckily YAPE::Regex::Explain handles these

use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(
'\b\$AVG'
)->explain;
__END__
The regular expression:

(?-imsx:\b\$AVG)

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 a word char (\w) and
                           something that is not a word char
----------------------------------------------------------------------
  \$                       '$'
----------------------------------------------------------------------
  AVG                      'AVG'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(
'\w?\$AVG\b'
)->explain;
__END__The regular expression:

(?-imsx:\w?\$AVG\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):
----------------------------------------------------------------------
  \w?                      word characters (a-z, A-Z, 0-9, _)
                           (optional (matching the most amount
                           possible))
----------------------------------------------------------------------
  \$                       '$'
----------------------------------------------------------------------
  AVG                      'AVG'
----------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

Comment on Re^3: regex not matching special char Select or Download Code

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Re^4: regex not matching special char by mnooning (Beadle) on Dec 14, 2012 at 12:33 UTC
Thanks for the tip on YAPE::Regex::Explain. As kennethk pointed out - reading between the lines - the key is to know that a back slashed special character will not be taken as a word character, and hence will be seen as a word boundary itself. That is why the simple \b does not work. Armed with a definitive answer as to what is happening, a simple work around can be constructed. In my case the strings I am looking for are actual directory names. I can split on the directory separator. Thanks again.	[reply]

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Re^4: regex not matching special char
by mnooning (Beadle) on Dec 14, 2012 at 12:33 UTC

Thanks for the tip on YAPE::Regex::Explain.

As kennethk pointed out - reading between the lines - the key is to know that a back slashed special character will not be taken as a word character, and hence will be seen as a word boundary itself. That is why the simple \b does not work.

Armed with a definitive answer as to what is happening, a simple work around can be constructed. In my case the strings I am looking for are actual directory names. I can split on the directory separator.

[reply]