perl - regex to match word boundary beginning with special characters

Question

I have regex that matches words fine except if they contain a special character such as ~Query which is the name of a member of a C++ class. Need to use word boundary as shown below for member names that are single characters. $key =~ /$match/

I tried numerous expressions I thought would work such as /[~]*$match/ or /[~]*$match/

Is it possible to put a word boundary on words that may contain a special character?

Answer 1

is short for

(?:(?<!w)(?=w)|(?<=w)(?!w))

If you want to treat ~ as a word character, change w to [w~].

(?:(?<![w~])(?=[w~])|(?<=[w~])(?![w~]))

Example usage:

my $word_char = qr/[w~]/;
my $boundary  = qr/(?<!$word_char)(?=$word_char)
                  |(?<=$word_char)(?!$word_char)/x;

$key =~ /$boundary$match$boundary/

If we know $match can only match something that starts and ends with a $word_char, we can simplify as follows:

my $word_char   = qr/[w~]/;
my $start_bound = qr/(?<!$word_char)/;
my $end_bound   = qr/(?!$word_char)/;

$key =~ /$start_bound$match$end_bound/

This is simple enough that we can inline.

$key =~ /(?<![w~])$match(?![w~])/