Regular expression: match start or whitespace

Question

Can a regular expression match whitespace or the start of a string?

I\'m trying to replace currency the abbreviation GBP with a £ symbol. I

Answer 1

It works in Perl:

$text = 'GBP 5 off when you spend GBP75';
$text =~ s/(\W|^)GBP([\W\d])/$1\$$2/g;
printf "$text\n";

The output is:

$ 5 off when you spend $75

Note that I stipulated that the match should be global, to get all occurrences.