gistfile1.txt

We have a list of keywords that we want to match against series of text. 
We use CPAN module Regexp::Trie to compile it into a regular expression.
For instance, if we have keywords "mac", "apple" and "android", we'll get 

  $re = qr/(?-xism:(?:a(?:ndroid|pple)|mac))/;

Because when we have "mac" in the keyword, we don't want to match against
"machines", so when we actually match against a text we use \b the zero-width
word boundary class, which works well with ASCII word chars at least.

  @match = $text =~ /\b($re)\b/g;

So far, so good.

However when we have punctuation characters at the beginning or end of the 
keyword we add to the TRIE itself, like "#android", this \b gets in the way, 
since '#' is not a word character. 

  my $rt = Regexp::Trie->new;
  $rt->add($_) for qw( #android #apple mac );
  $re = $rt->regexp; # qr/(?-xism:(?:\#a(?:ndroid|pple)|mac))/
  $text = "I love #android";
  my @tags = $text =~ /\b($re)\b/g; # @tags is empty

The result is that it doesn't really match those hash tags that appear after
a whitespace (most of the time) or the beginning of the text.

I'm trying to work around this by changing the matcher to this:

  @match = $text =~ /(?:^|\b|\s)($re)(?:$|\b|\s)/g;

as ugly as it looks, it seems to work. Any suggestions to make it look & work better?

I'm not sure if I got your point right because /\b($re)\b/g DOES match against '#mac'.
Is it that you want to capture '#' as well as the word? If so,

/(?<=\s)([#]?$re)\b/

is the regexp you are looking for.

Dan the Regular Expressionist

No - sorry i guess the example was confusing, but if the TRIE contains '#mac' (containing # itself) then \b will NOT match.

my $rt = Regexp::Trie->new;
$rt->add($_) for qw( #mac #win #unix );
my $re = $rt->regexp;

my $text = "I want #mac";
my @m = $text =~ /\b($re)\b/g;
# @m is empty